appDisplay: Update folder dialog field before ungrabbing

Noticed while working on customizable folders. Calling GrabHelper.ungrab()
ends up calling FolderDialog.popdown(), but at this point the '_isOpen'
field isn't updated yet, so we end up calling popdown() twice.

Update the '_isOpen' field before ungrabbing.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1332

js/ui/appDisplay.js

@@ -1782,8 +1782,8 @@ var AppFolderDialog = GObject.registerClass({
         this._zoomAndFadeOut();
         this._showFolderLabel();
 
-        this._grabHelper.ungrab({ actor: this });
         this._isOpen = false;
+        this._grabHelper.ungrab({ actor: this });
         this.emit('open-state-changed', false);
     }
 });