core: Hide close dialog before destroying

The MetaCloseDialog implementation object may stay artifically alive
for a longer period. This was usually fine till gnome-shell commit
b03bcc85aad, as the check_alive() timeout will keep running even
though the window went unmanaged/destroyed, leading to crashes.

In order to fix this, forcibly hide the dialog if it is visible and
the window is being unmanaged, so the timeout is stopped in time.


(cherry picked from commit 6abe4703c7)

src/core/delete.c

@@ -115,5 +115,8 @@ meta_window_kill (MetaWindow *window)
 void
 meta_window_free_delete_dialog (MetaWindow *window)
 {
+  if (window->close_dialog &&
+      meta_close_dialog_is_visible (window->close_dialog))
+    meta_close_dialog_hide (window->close_dialog);
   g_clear_object (&window->close_dialog);
 }