LightingShaderGen: Always calculate lighting for both color channels

Cel-damage uses the color from the lighting stage of the vertex pipeline
as texture coordinates, but sets numColorChans to zero.

We now calculate the colors in all cases, but override the color before
writing it from the vertex shader if numColorChans is set to a lower value.

Source/Core/VideoCommon/PixelShaderGen.cpp

@@ -643,7 +643,7 @@ ShaderCode GeneratePixelShaderCode(APIType ApiType, const ShaderHostConfig& host
     // out.SetConstantsUsed(C_PLIGHTS, C_PLIGHTS+31); // TODO: Can be optimized further
     // out.SetConstantsUsed(C_PMATERIALS, C_PMATERIALS+3);
     GenerateLightingShaderCode(out, uid_data->lighting, uid_data->components << VB_COL_SHIFT,
-                               uid_data->numColorChans, "colors_", "col");
+                               "colors_", "col");
   }
 
   // HACK to handle cases where the tex gen is not enabled