[gtk+/gtk-3-14] GtkMenuSectionBox: Add a clarifying assertion

[Matthias Clasen <matthiasc src gnome org>]

commit 9eef97fe1cbee8b469c76ae9fef84751d4b60d19
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Jul 17 20:15:24 2015 -0400

    GtkMenuSectionBox: Add a clarifying assertion
    
    This assertion helps coverity see what is clear to us.

 gtk/gtkmenusectionbox.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkmenusectionbox.c b/gtk/gtkmenusectionbox.c
index 97eeb5d..957441f 100644
--- a/gtk/gtkmenusectionbox.c
+++ b/gtk/gtkmenusectionbox.c
@@ -262,6 +262,7 @@ open_submenu (GtkWidget *button,
 
   focus = GTK_WIDGET (g_object_get_data (G_OBJECT (button), "focus"));
   get_ancestors (focus, GTK_TYPE_STACK, &stack, &child);
+  g_assert (stack != NULL && child != NULL);
   gtk_stack_set_visible_child (GTK_STACK (stack), child);
   gtk_widget_grab_focus (focus);
 }