closeDialog: Close existing dialogs on shutdown

Otherwise mutter will request to hide the dialog when the meta
context is destroyed, but at the JS context has already shut down,
resulting in a crash.

Close https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/7328

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3117>

js/ui/closeDialog.js

@@ -166,6 +166,9 @@ export const CloseDialog = GObject.registerClass({
         this._addWindowEffect();
         this._initDialog();
 
+        global.connectObject(
+            'shutdown', () => this._onWait(), this._dialog);
+
         this._dialog._dialog.scale_y = 0;
         this._dialog._dialog.set_pivot_point(0.5, 0.5);