fix shader for NVIDIA cards on mac

git-svn-id: https://dng.biozentrum.unibas.ch/svn/openstructure/branches/new_gfx@2276 5a81b35b-ba03-0410-adc8-b2c5c5119f08

modules/gfx/src/shader/fraglight_vs.glsl

@@ -21,7 +21,7 @@ void main()
     // ambient occlusion and color terms
     ambient_color = gl_MultiTexCoord0;
   } else {
-    ambient_color.rgb = gl_Color;
+    ambient_color.rgb = gl_Color.rgb;
     ambient_color.a = 1.0;
   }
   gl_FrontColor=gl_Color;