Make 'gcl diff emptychange' show nothing if given change, |emptychange|, does...

gcl.py

 #!/usr/bin/python
 # Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 # Wrapper script around Rietveld's upload.py that groups files into
 # changelists.
 
 import getpass
 import os
@@ skipping 1265 matching lines @@
     # argument to trychange.py.
     if change_info.GetFiles():
       args = argv[3:]
     else:
       change_info = None
       args = argv[2:]
     TryChange(change_info, args, swallow_exception=False)
   else:
     # Everything else that is passed into gcl we redirect to svn, after adding
     # the files. This allows commands such as 'gcl diff xxx' to work.
+    if command == "diff" and not change_info.GetFileNames():
+      return 0
     args =["svn", command]
     root = GetRepositoryRoot()
     args.extend([os.path.join(root, x) for x in change_info.GetFileNames()])
     RunShell(args, True)
   return 0
 
 
 if __name__ == "__main__":
   sys.exit(main())