Duke3D: Fix riding OOZ sprites and stacking pipebombs to behave like DOS
This addresses two related problems:
Fixes #105 by addressing a mistake in previous MR that tried to fix the OOZ problem, and by skipping the getzrange checksum for OOZ sprites.
Fixes the problem described in: https://forums.duke4.net/topic/11665-dukevr-red-mission-2/
The pipebombs can currently no longer be stacked, which originated from a change in
VM_Fall(). Secondly, like OOZ sprites, pipebombs used to be able to push each other upwards. This was also broken by the checksum case, and is required to beat the map in the above link.
The fact that the getzrange checksum alters semantics, when it was originally intended as an optimization, may need to be addressed in a future commit.