Fix: Crash when closing window while Outliner shows screens

Steps to reproduce were:
* From factory settings, change Outliner Display Mode to "Blender File"
* Open "Screens" item, make sure all listed screens are visible
* Open Preference window, close it
* Mouse hover the outliner -> crash

Fix is to force an Outliner tree rebuild when closing screens.

source/blender/windowmanager/intern/wm_window.c

@@ -463,6 +463,7 @@ void wm_window_close(bContext *C, wmWindowManager *wm, wmWindow *win)
 
     BLI_assert(BKE_workspace_layout_screen_get(layout) == screen);
     BKE_workspace_layout_remove(bmain, workspace, layout);
+    WM_event_add_notifier(C, NC_SCREEN | ND_LAYOUTDELETE, NULL);
   }
 }