Use half-Lambert lighting iff grid lighting is used

Half-Lambert lighting makes goes well with the light grid:
the single light direction is a crude approximation, so it makes
sense to soften the directionality.

For now this only changes anything for the `r_lightMode 2` debug
option, but it may be useful for implementing grid lighting for
BSP entities later.

Author: slipher

src/engine/renderer/glsl_source/computeLight_fp.glsl

@@ -90,7 +90,7 @@ void computeDeluxeLight( vec3 lightDir, vec3 normal, vec3 viewDir, vec3 lightCol
 	// clamp( NdotL, 0.0, 1.0 ) is done below
 	float NdotL = dot( normal, lightDir );
 
-	#if !defined(USE_BSP_SURFACE) && defined(r_halfLambertLighting)
+	#if defined(USE_GRID_LIGHTING) && defined(r_halfLambertLighting)
 		// http://developer.valvesoftware.com/wiki/Half_Lambert
 		NdotL = NdotL * 0.5 + 0.5;
 		NdotL *= NdotL;