[gnome-sudoku] Hide the Back button in new game screen at startup

[Parin Porecha <parinporecha src gnome org>]

commit c550524aef68d2709b9290820ebc9fc52eb4a52e
Author: Parin Porecha <parinporecha gmail com>
Date:   Mon Aug 18 20:33:29 2014 +0200

    Hide the Back button in new game screen at startup

 src/gnome-sudoku.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/gnome-sudoku.vala b/src/gnome-sudoku.vala
index 7d1880c..b925659 100644
--- a/src/gnome-sudoku.vala
+++ b/src/gnome-sudoku.vala
@@ -277,7 +277,7 @@ public class Sudoku : Gtk.Application
     private void show_new_game_screen ()
     {
         main_stack.set_visible_child_name ("start_box");
-        back_button.visible = true;
+        back_button.visible = game != null;
         undo_redo_box.visible = false;
         header_bar_subtitle = header_bar.get_subtitle ();
         header_bar.set_subtitle (null);