[f-spot] Fix build error with recent gtk-sharp

[Stephen Shaw <sshaw src gnome org>]

commit c42843b7c17141c6a0aa6f0605e0e2433b5a0dac
Author: Stephen Shaw <sshaw decriptor com>
Date:   Mon May 13 23:17:45 2013 -0600

    Fix build error with recent gtk-sharp

 src/Clients/MainApp/FSpot/GroupSelector.cs |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/Clients/MainApp/FSpot/GroupSelector.cs b/src/Clients/MainApp/FSpot/GroupSelector.cs
index b1e4993..63edd84 100644
--- a/src/Clients/MainApp/FSpot/GroupSelector.cs
+++ b/src/Clients/MainApp/FSpot/GroupSelector.cs
@@ -467,7 +467,7 @@ namespace FSpot {
                                bounds.Height = selector.background.Height;
                                bounds.Y = selector.background.Y;
                                bounds.X = selector.BoxX (item);
-                               bounds.Width = Math.Max (selector.BoxX (item + 1) - bounds.X, 1);
+                               bounds.Width = Math.Max (selector.BoxX (item + 1) - selector.BoxX (item), 1);
 
                                if (item < 0 || item > selector.box_counts.Length - 1)
                                        return;