Fix #11644: Off by one error/buffer over-read in StrMakeValid (#11645)

* Fix #11644: Off by one error in StrMakeValid UTF-8 decode overrun detection

* Fix #11644: Off by one error in StrMakeValid buffer last character

* Fix: Unnecessary string duplication at StrMakeValid call sites

Fix cda6f24f: don't ignore binary-dir if it happens to be working-dir (#11431)

Some of our code ignores the SP_WORKING_DIR for some actions, which
means that if, for example, your SP_BINARY_DIR is the same as your
SP_WORKING_DIR, neither is scanned.

Instead, only add SP_WORKING_DIR if it is unique.

Codechange: use the C++ std::getenv over the POSIX/C getenv

The C++ std::getenv is guaranteed thread-safe by the C++11 specification,
whereas the POSIX/C getenv might not be thread-safe by the C11 specification.

Change: move sensitive information to secrets.cfg and private information to private.cfg

We often ask people for their openttd.cfg, which now includes their
passwords, usernames, etc. It is easy for people to overlook this,
unwillingly sharing information they shouldn't.

By splitting this information over either private.cfg or secrets.cfg,
we make it more obvious they shouldn't be sharing those files, and
hint to what is inside them.

Add: '-X' option to ignore global folders in the search path (#9341)

This is extreme useful for automated testing. Without this, OpenTTD
will always look in your personal-dir (like ~/.local/share/openttd
or %USER%\Documents\OpenTTD). For most users this is exactly what
we want, that there is a shared place for all their files.

However, for automated testing this is rather annoying, as your
local development files influence the automated test. As such,
'-X' counters this, and only gives the local folders. This is
especially useful in combination with '-x' and '-c'.

Codechange: [OSX] Re-arrange the OSX video driver code by combining all drawing code and moving the window/event handling to a different file.

This is just a code move/rename, not a functionality change.

Add: always set PERSONAL_DIR "/content_download" in search path (#8481)

This means that if you start OpenTTD with "-c" to indicate another
location to store files, it can still read the content you already
downloaded from your PERSONAL_DIR. This folder is, however,
read-only.

This is useful for situations where you downloaded OpenGFX via
the content-service, but want to run the regression or want to
run with a clean configuration. With this change, you no longer
need to download OpenGFX again.

Remove: Remnants of PSP support.

No active target is that limited in concurrent file descriptors.

Fix: set SP_WORKING_DIR earlier with '-c'

On Windows, relative folders don't work so well. So we need to
lookup the full path. This is best done in DetermineBasePaths()
and as a bonus that only sets SP_WORKING_DIR once.

Fix: change the working-dir searchpath when using '-c'

Basically, with '-c' you now create a sandbox. It will still use
your personal-dir and global-dir to find files you installed there,
but all new files are stored with a base folder identical to the
folder the configuration is in.

This is a bit of an old bug, that we many have tried to solve in
various of different ways. The code has grown sufficiently complex
that it is hard to see what consequences of actions are. This is
in my opinion the most harmless solution, while increasing the
usefulness of the '-c' flag.

In essence, the problem was that empty folders were always created
in the directory where the configuration was, but as that directory
wasn't added to any searchpath, files weren't stored there, unless
by accident it was a folder already on the searchpath. For example,
if you do './openttd -c local.cfg', it did work as expected. But
in the more generic variant, it did not.

With this patch, you can run './openttd -c /new/folder/local.cfg',
and it will create and prepare that folder to receive new files.

'content_download' is also stored in the directory the
configuration is in; this was already the case. Important to
note that there is only one search-path for 'content_download'.
In other words, when using '-c', it will not look in '~/.openttd'
inside the 'content_download' folder.

Codechange: to create or not to create a folder, that is the question

This was just weird. With XDG _personal_dir was created already,
but later on it was checked if it was different from config_dir,
and the creation was skipped. All this checking and validation
makes my head spin .. let's make it a bit more simple.

Change: Log when rejecting a TAR archive for extraction

Based on report in <https://www.tt-forums.net/viewtopic.php?f=31&t=87374>;

Remove: ENABLE_NETWORK switch

This switch has been a pain for years. Often disabling broke
compilation, as no developer compiles OpenTTD without, neither do
any of our official binaries.

Additionaly, it has grown so hugely in our codebase, that it
clearly shows that the current solution was a poor one. 350+
instances of "#ifdef ENABLE_NETWORK" were in the code, of which
only ~30 in the networking code itself. The rest were all around
the code to do the right thing, from GUI to NewGRF.

A more proper solution would be to stub all the functions, and
make sure the rest of the code can simply assume network is
available. This was also partially done, and most variables were
correct if networking was disabled. Despite that, often the #ifdefs
were still used.

With the recent removal of DOS, there is also no platform anymore
which we support where networking isn't working out-of-the-box.

All in all, it is time to remove the ENABLE_NETWORK switch. No
replacement is planned, but if you feel we really need this option,
we welcome any Pull Request which implements this in a way that
doesn't crawl through the code like this diff shows we used to.

Remove: DOS support

In 10 years there was no active development on DOS. Although it
turned out to still work, the FPS was very bad. There is little
interest in the current community to look into this.

Further more, we like to switch to c++11 functions for threads,
which are not implemented by DJGPP, the only current compiler
for DOS.

Additionally, DOS is the only platform which does not support
networking. It is the reason we have tons of #ifdefs to support
disabling networking.

By removing DOS support, we can both use c++11 functions for threads,
and remove all the code related to disabling network. Sadly, this
means we have to see DOS go.

Of course, if you feel up for the task, simply revert this commit,
and implement stub c++11 functions for threads and stub functions
for networking. We are more than happy to accept such Pull Request.

Codechange: check if a define is set directly, instead of indirectly

config.lib happens to set GLOBAL_DATA_DIR in case it is not DOS
and not OS2, but this kind of deduction is annoying to maintain.
It is better to just check if the define you want to use is set,
and leave it to config.lib to set it or not depending on the OS.

Remove: MorphOS / AmigaOS support

In 10 years there is no commit to change how MorphOS works, and we
have no active maintainer for it. It is unlikely it works in its
current state (but not impossible).

With the arrival of SDL2 (and removal of SDL), MorphOS is no longer
support. There is an SDL2 port for MorphOS, but it is not maintained
by upstream SDL2, and nobody can currently test it out.

If anyone wants to re-add MorphOS, please do (revert this patch,
fix the problems, and create a Pull Request). If you need any help
doing so, let us know! It is not that we don't like MorphOS, it is
that we don't have anyone fixing the problems :(