gcl delete <non-existent change> won't throw an exception anymore

gcl.py

 #!/usr/bin/env python
 # Copyright (c) 2011 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 simplifies working with groups
 of files.
 """
 
@@ skipping 1286 matching lines @@
 def CMDdescription(change_info):
   """Prints the description of the specified change to stdout."""
   print change_info.description
   return 0
 
 
 def CMDdelete(args):
   """Deletes a changelist."""
   if not len(args) == 1:
     ErrorExit('You need to pass a change list name')
-  os.remove(GetChangelistInfoFile(args[0]))
+  filepath = GetChangelistInfoFile(args[0])
+  if not os.path.isfile(filepath):
+    ErrorExit('You need to pass a valid change list name')
+  os.remove(filepath)
   return 0
 
 
 def CMDtry(args):
   """Sends the change to the tryserver to do a test run on your code.
 
   To send multiple changes as one path, use a comma-separated list of
   changenames. Use 'gcl help try' for more information!"""
   # When the change contains no file, send the "changename" positional
   # argument to trychange.py.
@@ skipping 131 matching lines @@
       raise
     print >> sys.stderr, (
         'AppEngine is misbehaving and returned HTTP %d, again. Keep faith '
         'and retry or visit go/isgaeup.\n%s') % (e.code, str(e))
     return 1
 
 
 if __name__ == "__main__":
   fix_encoding.fix_encoding()
   sys.exit(main(sys.argv[1:]))