Fake floor/ceiling planes don't work if there's a colormap in the same sector

This bug is present in both renderers. Sprites still get cut off like normal and drop shadows appear at the proper height (of the fake floor).

changed title from Fake floor/ceiling planes don't render if there's a colormap in the same sector to Fake floor/ceiling planes don't work if there's a colormap in the same sector

added Rendering and removed OpenGL renderer Software renderer labels