Fix: do not update a RV's Z-position when stationary while turning

When the direction of a RV changes the Z-position update logic was called,
which did nothing to the Z-position because that is only changed every other
step. By chance/luck this never triggered with RV's turning around, until
making the partial Z calculations consistent and moving the locations where
the Z-position is changed, causing the Z-position to be changed twice for
the RV that stayed at the same location.