[banshee] [ContextPane] Fix crash if active removed (bgo#613277)

[Gabriel Burt <gburt src gnome org>]

commit 630efc31aa862f785c4085973f542bee70ee35a4
Author: Gabriel Burt <gabriel burt gmail com>
Date:   Thu Mar 18 17:16:34 2010 -0700

    [ContextPane] Fix crash if active removed (bgo#613277)

 .../Banshee.ContextPane/ContextPane.cs             |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/src/Core/Banshee.ThickClient/Banshee.ContextPane/ContextPane.cs b/src/Core/Banshee.ThickClient/Banshee.ContextPane/ContextPane.cs
index 2a92568..88b0a60 100644
--- a/src/Core/Banshee.ThickClient/Banshee.ContextPane/ContextPane.cs
+++ b/src/Core/Banshee.ThickClient/Banshee.ContextPane/ContextPane.cs
@@ -173,6 +173,10 @@ namespace Banshee.ContextPane
 
         private void OnActivePageStateChanged (ContextState state)
         {
+            if (active_page == null || !pane_pages.ContainsKey (active_page)) {
+                return;
+            }
+
             if (state == ContextState.NotLoaded)
                 notebook.CurrentPage = notebook.PageNum (no_active);
             else if (state == ContextState.Loading)