Don't try to fog flares with fogNum 0

fogNum 0 means no fog. Shaders don't try to apply fog color if fogNum is 0.

This was done to make things more consistent and fix a crash in iortcw MP using a user made map on GNU/Linux x86_64.
Only allow model meshes to have SHADER_MAX_VERTEXES - 1 vertexes

The last index is used to check for buffer overflows. See RB_CheckOverflow and RB_EndSurface.
Fix IQM tess buffer overflow

Set the variables that use tess.numVertexes after calling RB_CHECKOVERFLOW() as it may set tess.numVertexes to 0!

Could cause visual issues and error "RB_EndSurface() - SHADER_MAX_VERTEXES hit".
Merge remote-tracking branch 'ioquake3/master'

Conflicts:
	code/renderergl1/tr_flares.c
	code/renderergl2/tr_flares.c