[gtk/wip/muktupavels/fix-critical-warning-master] menu: fix critical warning

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 686552148b97eacb381decd851ea81721a4e5e7d
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Thu Nov 14 18:02:36 2019 +0200

    menu: fix critical warning
    
    https://gitlab.gnome.org/GNOME/gnome-shell/issues/1899

 gtk/gtkmenu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtkmenu.c b/gtk/gtkmenu.c
index c95036fdd1..16a03dbea2 100644
--- a/gtk/gtkmenu.c
+++ b/gtk/gtkmenu.c
@@ -2077,7 +2077,9 @@ menu_grab_transfer_surface_destroy (GtkMenu *menu)
       g_object_set_data (G_OBJECT (menu), I_("gtk-menu-transfer-surface"), NULL);
 
       widget_surface = gtk_native_get_surface (gtk_widget_get_native (GTK_WIDGET (menu)));
-      g_object_set_data (G_OBJECT (widget_surface), I_("gdk-attached-grab-surface"), surface);
+
+      if (widget_surface != NULL)
+        g_object_set_data (G_OBJECT (widget_surface), I_("gdk-attached-grab-surface"), surface);
     }
 }