macosx: use optimized drawing for the main window as well (in addition to the detached vout window)

(cherry picked from commit ca0752e4ff27c29b63f95f579378a4c1fa983488)

modules/gui/macosx/MainWindow.m

@@ -131,6 +131,7 @@ static VLCMainWindow *_o_sharedInstance = nil;
 #endif
     i_lastShownVolume = -1;
     t_hide_mouse_timer = nil;
+    [self useOptimizedDrawing: YES];
 
     [o_play_btn setToolTip: _NS("Play/Pause")];
     [o_detached_play_btn setToolTip: [o_play_btn toolTip]];