BUG: fence textures on func's don't render

[dsvensson]

This classic renderer bug was introduced in this commit as an attempt to improve lighting from the looks of before/after screenshots. The side effect was that most of the brush entity no longer renders. Support for this case in the modern renderer has never existed.

Output before/after the above mentioned commit:

[dsvensson]

Modern renderer is fixed by #833, but the old renderer needs some other fix, most likely getting it to use the alphachain properly.