[gtkmm] demos/gtk-demo/demos.h: Add an end element to child1[]

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 56089b8ab83eec47e2c550e2182c792369c961e4
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Sun Sep 6 19:25:56 2020 +0200

    demos/gtk-demo/demos.h: Add an end element to child1[]
    
    DemoWindow::fill_tree() needs an end element with nullptr to be able to
    safely find the end of the array.

 demos/gtk-demo/demos.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/demos/gtk-demo/demos.h b/demos/gtk-demo/demos.h
index 1a55eacd..273c794e 100644
--- a/demos/gtk-demo/demos.h
+++ b/demos/gtk-demo/demos.h
@@ -49,7 +49,8 @@ Demo child0[] =
 
 Demo child1[] =
 {
-  { "Application launcher", "example_listview_applauncher.cc", sigc::ptr_fun(&do_listview_applauncher), 
nullptr }
+  { "Application launcher", "example_listview_applauncher.cc", sigc::ptr_fun(&do_listview_applauncher), 
nullptr },
+  { nullptr, nullptr, type_slotDo(), nullptr }
 };
 
 Demo testgtk_demos[] =