[gnome-shell] UserMenu: fix disconnecting a signal that was never connected

[Giovanni Campagna <gcampagna src gnome org>]

commit 355ec9ceca6ef15f72bedf854c8c00a382ff09b8
Author: Giovanni Campagna <gcampagna src gnome org>
Date:   Tue Aug 7 16:33:02 2012 +0200

    UserMenu: fix disconnecting a signal that was never connected
    
    If a disabled account is removed, we receive account-removed without
    ever seeing account-enabled, and thus _changingId is undefined.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=681382

 js/ui/userMenu.js |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/js/ui/userMenu.js b/js/ui/userMenu.js
index 7f8d544..9522134 100644
--- a/js/ui/userMenu.js
+++ b/js/ui/userMenu.js
@@ -654,8 +654,10 @@ const UserMenuButton = new Lang.Class({
     },
 
     _onAccountRemoved: function(accountMgr, account) {
-        account.disconnect(account._changingId);
-        account._changingId = 0;
+        if (account._changingId) {
+            account.disconnect(account._changingId);
+            account._changingId = 0;
+        }
         this._updateChangingPresence();
     },