qt4 and skins2: fix resizing issue when zooming in/out and is_display_filled is enabled

returning VLC_EGENERIC is no problem, since the vout system is an observer of the change in size and will report the real situation.
returning VLC_SUCCESS is wrong in an asynchronous environmenent, as resizing is only performed later on (or not) depending on GUI configuration.

modules/gui/qt4/main_interface.cpp

@@ -890,7 +890,7 @@ int MainInterface::controlVideo( int i_query, va_list args )
         unsigned int i_height = va_arg( args, unsigned int );
         emit askVideoToResize( i_width, i_height );
         emit askUpdate();
-        return VLC_SUCCESS;
+        return VLC_EGENERIC;
     }
     case VOUT_WINDOW_SET_ON_TOP:
     {

modules/gui/skins2/src/vout_manager.cpp

@@ -358,7 +358,7 @@ int VoutManager::controlWindow( struct vout_window_t *pWnd,
                    AsyncQueue::instance( pThis->getIntf() );
                 pQueue->push( CmdGenericPtr( pCmd ) );
             }
-            return VLC_SUCCESS;
+            return VLC_EGENERIC;
         }
 
         case VOUT_WINDOW_SET_FULLSCREEN: