nForum Delete Media Fix

diff -Nur nforum_547b7d6d7faf/nForum.BusinessLogic/nForumEvents.cs nforum_547b7d6d7faf_mod/nForum.BusinessLogic/nForumEvents.cs
--- nforum_547b7d6d7faf/nForum.BusinessLogic/nForumEvents.cs	2011-02-18 06:40:12.000000000 +0100
+++ nforum_547b7d6d7faf_mod/nForum.BusinessLogic/nForumEvents.cs	2011-11-17 15:43:04.416734700 +0100
@@ -29,6 +29,8 @@
         {
             #region Forum Topic Move Events
             var sid = (CMSNode)sender;
+            if (sid.nodeObjectType != Document._objectType)
+                return;
             var s = new Document(sid.Id);
 
             if (s.ContentType.Alias == "ForumTopic" && s.ParentId != -20)