Add some error checking to CMDpassthru for invalid arguments.

TEST=Run a passthru command like gcl di or gcl revert without a changelist name. Ensure that gcl exits with an error message.
BUG=none

Review URL: http://codereview.chromium.org/8413015

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@107663 0039d316-1c4b-4281-b951-d872f2087c98

gcl.py

@@ -1339,6 +1339,9 @@ def CMDpassthru(args):
 
   It assumes a change list name is passed and is converted with the files names.
   """
+  if not args or len(args) < 2:
+    ErrorExit("You need to pass a change list name for this svn fall-through "
+              "command")
   cl_name = args[1]
   args = ["svn", args[0]]
   if len(args) > 1: