Fix git cl checkout when no branch has issues.

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 distutils.version import LooseVersion
@@ skipping 4532 matching lines @@
     parser.print_help()
     return 1
 
   issue_arg = ParseIssueNumberArgument(args[0])
   if not issue_arg.valid:
     parser.print_help()
     return 1
   target_issue = str(issue_arg.issue)
 
   def find_issues(issueprefix):
-    key_and_issues = [x.split() for x in RunGit(
-        ['config', '--local', '--get-regexp', r'branch\..*\.%s' % issueprefix])
-        .splitlines()]
-    for key, issue in key_and_issues:
+    output = RunGit(['config', '--local', '--get-regexp',
+                     r'branch\..*\.%s' % issueprefix],
+                     error_ok=True)
+    for key, issue in [x.split() for x in output.splitlines()]:
       if issue == target_issue:
         yield re.sub(r'branch\.(.*)\.%s' % issueprefix, r'\1', key)
 
   branches = []
   for cls in _CODEREVIEW_IMPLEMENTATIONS.values():
     branches.extend(find_issues(cls.IssueSettingPrefix()))
   if len(branches) == 0:
     print 'No branch found for issue %s.' % target_issue
     return 1
   if len(branches) == 1:
@@ skipping 67 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)