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

R=dpranke@chromium.org
BUG=
TEST=

Review URL: http://codereview.chromium.org/6735029

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@80337 0039d316-1c4b-4281-b951-d872f2087c98

gcl.py

@@ -1304,7 +1304,10 @@ 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