popupMenu: block input events when menu is closing

At the moment gnome-shell can get really confused if a menu is
fading out and gets clicked.

It can lead to mouse pointer input getting stuck until the shell
is restarted.

This commit addresses the problem by ignoring input events that
come in when the menu is closing.

js/ui/popupMenu.js

@@ -123,12 +123,18 @@ var PopupBaseMenuItem = new Lang.Class({
     },
 
     _onButtonReleaseEvent(actor, event) {
+        if (this._parent && !this._parent.isOpen)
+            return Clutter.EVENT_STOP;
+
         this.actor.remove_style_pseudo_class ('active');
         this.activate(event);
         return Clutter.EVENT_STOP;
     },
 
     _onTouchEvent(actor, event) {
+        if (this._parent && !this._parent.isOpen)
+            return Clutter.EVENT_STOP;
+
         if (event.type() == Clutter.EventType.TOUCH_END) {
             this.actor.remove_style_pseudo_class ('active');
             this.activate(event);
@@ -141,6 +147,9 @@ var PopupBaseMenuItem = new Lang.Class({
     },
 
     _onKeyPressEvent(actor, event) {
+        if (this._parent && !this._parent.isOpen)
+            return Clutter.EVENT_STOP;
+
         let state = event.get_state();
 
         // if user has a modifier down (except capslock and numlock)