shell-gtk-embed: Fix NULL pointer dereference

Clutter will try to unmap during a dispose if we have a parent, so if we
set our own actor to NULL before the chain up, we're going to attempt to
unmap our own NULL actor. Fix that by swapping the order in which we
chain up.

https://bugzilla.gnome.org/show_bug.cgi?id=672790

src/shell-gtk-embed.c

@@ -223,9 +223,9 @@ shell_gtk_embed_dispose (GObject *object)
 {
   ShellGtkEmbed *embed = SHELL_GTK_EMBED (object);
 
-  shell_gtk_embed_set_window (embed, NULL);
-
   G_OBJECT_CLASS (shell_gtk_embed_parent_class)->dispose (object);
+
+  shell_gtk_embed_set_window (embed, NULL);
 }
 
 static void