[gnome-shell] dnd: Don't pass null to ClutterActor.disconnect()

[Adel Gadllah <agadllah src gnome org>]

commit 7c534a87cfe8aeee220d068115a51c5281f3f5af
Author: Adel Gadllah <adel gadllah gmail com>
Date:   Mon Feb 28 22:34:19 2011 +0100

    dnd: Don't pass null to ClutterActor.disconnect()
    
    _ungrabActor disconnects the event signal handler but does not
    check whether it is connected before doing so which can result into
    an exception like:
    
    JS ERROR: !!!   Exception was: Error: disconnect() takes one arg, the signal handler id
    JS ERROR: !!!     lineNumber = '0'
    JS ERROR: !!!     fileName = 'gjs_throw'
    JS ERROR: !!!     stack = 'Error("disconnect() takes one arg, the signal handler id")@:0

 js/ui/dnd.js |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/js/ui/dnd.js b/js/ui/dnd.js
index 021cb2e..61776da 100644
--- a/js/ui/dnd.js
+++ b/js/ui/dnd.js
@@ -144,6 +144,8 @@ _Draggable.prototype = {
 
     _ungrabActor: function() {
         Clutter.ungrab_pointer();
+        if (!this._onEventId)
+            return;
         this.actor.disconnect(this._onEventId);
         this._onEventId = null;
     },