OpenGL2: Fix q3map2 lightstyles effects

Fixes World of Padman wop_trashmap.

For r_mergeLightmaps 1
- Fix tcMod transform on "map $lightmap" stages
- Fix external lightmap image texcoords if shader also has an internal
  lightmap

For r_sunlightMode 1
- Fix "tcGen lightmap" stages with blendFunc GL_SRC_ALPHA GL_ONE being
  converted to white image + modulate lightmap and drawing incorrectly

code/renderergl2/tr_bsp.c

@@ -497,6 +497,7 @@ static	void R_LoadLightmaps( lump_t *l, lump_t *surfs ) {
 }
 
 
+// If FatPackU() or FatPackV() changes, update FixFatLightmapTexCoords()
 static float FatPackU(float input, int lightmapnum)
 {
 	if (lightmapnum < 0)