Add a minor numerical improvement

Assets/ScriptableRenderPipeline/ShaderLibrary/AreaLighting.hlsl

         if (omega < HALF_PI)
         {
             // Partial horizon occlusion (case #2).
-            irradiance = e + INV_PI * g - (INV_PI * h);
+            irradiance = e + INV_PI * (g - h);
-            irradiance = INV_PI * g + (INV_PI * h);
+            irradiance = INV_PI * (g + h);
         }
     }