renderer: disable GLSL overbright on fullbright lightmode globally instead of doing it per-texture

It fixes rendering fullbright lightmap stages when light mode is not fullbright,
like the starchart512 hologram in procyon map.

Author: illwieckz

src/engine/renderer/tr_bsp.cpp

@@ -5179,9 +5179,9 @@ void RE_LoadWorldMap( const char *name )
 		}
 	}
 
-	/* Used in GLSL code for the GLSL implementation
-	without color clamping and normalization. */
-	if ( !tr.legacyOverBrightClamping )
+	/* Set GLSL overbright parameters if the legacy clamped overbright isn't used
+	and the lighting mode is not fullbright. */
+	if ( !tr.legacyOverBrightClamping && tr.lightMode != lightMode_t::FULLBRIGHT )
 	{
 		tr.mapLightFactor = pow( 2, tr.mapOverBrightBits );
 		tr.mapInverseLightFactor = 1.0f / tr.mapLightFactor;

src/engine/renderer/tr_shade.cpp

@@ -1128,7 +1128,7 @@ void Render_lightMapping( shaderStage_t *pStage )
 	// u_InverseLightFactor
 	/* HACK: use sign to know if there is a light or not, and
 	then if it will receive overbright multiplication or not. */
-	bool cancelOverBright = pStage->cancelOverBright || lightMode == lightMode_t::FULLBRIGHT;
+	bool cancelOverBright = pStage->cancelOverBright;
 	float inverseLightFactor = cancelOverBright ? tr.mapInverseLightFactor : -tr.mapInverseLightFactor;
 	gl_lightMappingShader->SetUniform_InverseLightFactor( inverseLightFactor );