[gtk] menu: Guard against NULL toplevel

[Timm Bäder <baedert src gnome org>]

commit d54321c1ca7da3d9b0a867b26f63340a48eba74c
Author: Timm Bäder <mail baedert org>
Date:   Tue Sep 26 07:10:39 2017 +0200

    menu: Guard against NULL toplevel
    
    This can happen, as indicated by GtkMenu explicitly connecting to
    ::destroy of its toplevel window. Do the same thing in GtkComboBox.

 gtk/gtkmenu.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)
---
diff --git a/gtk/gtkmenu.c b/gtk/gtkmenu.c
index a39aa42351..95562ab9fb 100644
--- a/gtk/gtkmenu.c
+++ b/gtk/gtkmenu.c
@@ -1384,11 +1384,14 @@ gtk_menu_detach (GtkMenu *menu)
   g_object_set_data (G_OBJECT (menu), I_(attach_data_key), NULL);
 
   /* Detach the toplevel window. */
-  g_signal_handlers_disconnect_by_func (toplevel,
-                                        (gpointer) menu_toplevel_attached_to,
-                                        menu);
-  if (gtk_window_get_attached_to (toplevel) == data->attach_widget)
-    gtk_window_set_attached_to (toplevel, NULL);
+  if (toplevel)
+    {
+      g_signal_handlers_disconnect_by_func (toplevel,
+                                            (gpointer) menu_toplevel_attached_to,
+                                            menu);
+      if (gtk_window_get_attached_to (toplevel) == data->attach_widget)
+        gtk_window_set_attached_to (toplevel, NULL);
+    }
 
   g_signal_handlers_disconnect_by_func (data->attach_widget,
                                         (gpointer) attach_widget_display_changed,