- Avoid iterating displayplayers to find view number and
prefer R_GetViewNumber.
- Iterate over all matching displayplayers if necessary,
instead of stopping at the first match.
- Ensures that column drawer doesn't read out of bounds
the brightmap column.
- Refactored code in r_segs.cpp, so it checks
R_TextureHasBrightmap.
- Added comments for plane brightmaps and sprite
brightmaps, that these are still error-prone.
