[gnome-chess] Fix crash when new game dialog is deleted

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 0c38c0d5811bc0f5d2ffb90dbe7001aacbda2588
Author: Michael Catanzaro <mike catanzaro gmail com>
Date:   Tue Jul 9 08:28:44 2013 -0500

    Fix crash when new game dialog is deleted
    
    https://bugzilla.gnome.org/show_bug.cgi?id=703857

 src/gnome-chess.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/gnome-chess.vala b/src/gnome-chess.vala
index c3d3087..8c21cbe 100644
--- a/src/gnome-chess.vala
+++ b/src/gnome-chess.vala
@@ -1086,7 +1086,7 @@ public class Application : Gtk.Application
             else if (result == Gtk.ResponseType.YES)
                 save_game (Gtk.Stock.DISCARD, Gtk.Stock.SAVE); /* Your very last chance to save */
             else
-                assert (result == Gtk.ResponseType.NO);
+                warn_if_fail (result == Gtk.ResponseType.NO || result == Gtk.ResponseType.DELETE_EVENT);
         }
 
         start_new_game ();