Make sure thread pool has at least 1 worker.

git_cl.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld and Gerrit."""
 
 from __future__ import print_function
@@ skipping 3055 matching lines @@
       yield fetch(changes[0])
 
       if not changes:
         # Exit early if there was only one branch to fetch.
         return
 
       changes_to_fetch = changes[1:]
       pool = ThreadPool(
           min(max_processes, len(changes_to_fetch))
               if max_processes is not None
-              else len(changes_to_fetch))
+              else max(len(changes_to_fetch), 1))
 
       fetched_cls = set()
       it = pool.imap_unordered(fetch, changes_to_fetch).__iter__()
       while True:
         try:
           row = it.next(timeout=5)
         except multiprocessing.TimeoutError:
           break
 
         fetched_cls.add(row[0])
@@ skipping 2017 matching lines @@
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   setup_color.init()
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)