when checking the previous tracker address for the torrent creator, don't use a blank address

NEWS

@@ -15,6 +15,7 @@ http://trac.transmissionbt.com/query?group=component&milestone=1.33
    + Fix small memory leaks
 - Mac
    + Rephrase "data not fully available" to "remaining time unknown"
+   + Fix bug where torrent file creation would fail because an extra blank tracker addresses was inserted
 - Daemon
    + Fix crash when adding nonexistent torrents via transmission-remote
 - GTK+

macosx/CreatorWindowController.m

@@ -115,9 +115,12 @@
             NSString * tracker;
             if ((tracker = [fDefaults stringForKey: @"CreatorTracker"]))
             {
-                [fTrackers addObject: tracker];
                 [fDefaults removeObjectForKey: @"CreatorTracker"];
-                [fDefaults setObject: fTrackers forKey: @"CreatorTrackers"];
+                if (![tracker isEqualToString: @""])
+                {
+                    [fTrackers addObject: tracker];
+                    [fDefaults setObject: fTrackers forKey: @"CreatorTrackers"];
+                }
             }
         }