[gnome-shell] popupMenu: Fix bubbling in the slider widget

[Jasper St. Pierre <jstpierre src gnome org>]

commit cc64091f9c54d87de311cbc246a368afaf73cc42
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Thu Feb 14 17:33:48 2013 -0500

    popupMenu: Fix bubbling in the slider widget
    
    https://bugzilla.gnome.org/show_bug.cgi?id=701755

 js/ui/popupMenu.js |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/js/ui/popupMenu.js b/js/ui/popupMenu.js
index fbe1e7e..a70b56f 100644
--- a/js/ui/popupMenu.js
+++ b/js/ui/popupMenu.js
@@ -621,7 +621,7 @@ const PopupSliderMenuItem = new Lang.Class({
 
     _startDragging: function(actor, event) {
         if (this._dragging) // don't allow two drags at the same time
-            return;
+            return false;
 
         this._dragging = true;
 
@@ -634,6 +634,8 @@ const PopupSliderMenuItem = new Lang.Class({
         let absX, absY;
         [absX, absY] = event.get_coords();
         this._moveHandle(absX, absY);
+
+        return true;
     },
 
     _endDragging: function() {