Fix mixed indentation in GraphicsUtil.cpp

To be fair, it was more on the level of entire functions using different
indentation than the surrounding code, but it's not consistent enough
for me to justify leaving it alone.

desktop_version/src/GraphicsUtil.cpp

@@ -384,7 +384,7 @@ SDL_Surface* ApplyFilter( SDL_Surface* _src )
 
         }
     }
-return _ret;
+    return _ret;
 }
 
 void FillRect( SDL_Surface* _surface, const int _x, const int _y, const int _w, const int _h, const int r, int g, int b )