[gnome-control-center] display: Avoid possible warning on exit

[Bastien Nocera <hadess src gnome org>]

commit f4c3d190bc5210418b65a6fe5c398cf99068eb91
Author: Bastien Nocera <hadess hadess net>
Date:   Thu Aug 23 14:22:19 2012 +0100

    display: Avoid possible warning on exit
    
    (gnome-control-center:8728): GLib-GObject-WARNING **: invalid (NULL) pointer instance
    
    (gnome-control-center:8728): GLib-GObject-CRITICAL **: g_signal_handler_disconnect: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed

 panels/display/cc-display-panel.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)
---
diff --git a/panels/display/cc-display-panel.c b/panels/display/cc-display-panel.c
index 78e06aa..9dbc276 100644
--- a/panels/display/cc-display-panel.c
+++ b/panels/display/cc-display-panel.c
@@ -169,9 +169,13 @@ cc_display_panel_finalize (GObject *object)
     g_object_unref (self->priv->clock_settings);
 
   shell = cc_panel_get_shell (CC_PANEL (self));
-  toplevel = cc_shell_get_toplevel (shell);
-  g_signal_handler_disconnect (G_OBJECT (toplevel),
-                               self->priv->focus_id);
+  if (shell != NULL)
+    {
+      toplevel = cc_shell_get_toplevel (shell);
+      if (toplevel != NULL)
+        g_signal_handler_disconnect (G_OBJECT (toplevel),
+                                     self->priv->focus_id);
+    }
 
   gnome_rr_labeler_hide (self->priv->labeler);
   g_object_unref (self->priv->labeler);