[gnome-mines/wip/theming-support] Fixed potential crasher

[Robert Roth <robertroth src gnome org>]

commit 13254fd9cf4360c8936141a3ec1c765c8d03cbf6
Author: Robert Roth <robert roth off gmail com>
Date:   Thu Jan 8 00:21:12 2015 +0200

    Fixed potential crasher

 src/minefield-view.vala |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/src/minefield-view.vala b/src/minefield-view.vala
index 861d7e5..faad916 100644
--- a/src/minefield-view.vala
+++ b/src/minefield-view.vala
@@ -592,9 +592,10 @@ public class MinefieldView : Gtk.Grid
 
     public void refresh()
     {
-        for (int i = 0; i < _minefield.width; i++)
-            for (int j = 0; j < _minefield.height; j++)
-                mines[i,j].refresh_icon ();
+        if (_minefield != null)
+            for (int i = 0; i < _minefield.width; i++)
+                for (int j = 0; j < _minefield.height; j++)
+                    mines[i,j].refresh_icon ();
     }
 
     public override bool key_release_event (Gdk.EventKey event)