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

gcl.py

Index: gcl.py
diff --git a/gcl.py b/gcl.py
index 6136d1c5a96ee6f198d37ed1606621294b854b90..2b63e36779bf0fe5ee3fdde133c5fb198cab79d0 100755
--- a/gcl.py
+++ b/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