[gnome-shell] autorunManager: Fix another regression

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

commit 457fb604ddeede1ec4d5b99e31ed280f3f2db0f5
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Wed Sep 5 13:46:55 2012 -0300

    autorunManager: Fix another regression
    
    We may not have a resident source to destroy if no mounts are found.

 js/ui/components/autorunManager.js |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/js/ui/components/autorunManager.js b/js/ui/components/autorunManager.js
index cf75cb1..38f93bc 100644
--- a/js/ui/components/autorunManager.js
+++ b/js/ui/components/autorunManager.js
@@ -169,7 +169,8 @@ const AutorunManager = new Lang.Class({
     },
 
     disable: function() {
-        this._residentSource.destroy();
+        if (this._residentSource)
+            this._residentSource.destroy();
         this._volumeMonitor.disconnect(this._mountAddedId);
         this._volumeMonitor.disconnect(this._mountRemovedId);
     },