git-cl: parse baseurl arguments eagerly

Currently, `git cl help baseurl` fails as it tries to execute the
subcommand, completely bypassing the help.

Parse the arguments early so that the help command runs cleanly for
baseurl.

Fixed: 1345909
Change-Id: Icad7aca6cdc7c9938e91a421cb72e08433a30fd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3776942
Auto-Submit: Thiago Perrotta <tperrotta@chromium.org>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

git_cl.py

@@ -3391,9 +3391,9 @@ def CMDcreds_check(parser, args):
 @metrics.collector.collect_metrics('git cl baseurl')
 def CMDbaseurl(parser, args):
   """Gets or sets base-url for this branch."""
+  _, args = parser.parse_args(args)
   branchref = scm.GIT.GetBranchRef(settings.GetRoot())
   branch = scm.GIT.ShortBranchName(branchref)
-  _, args = parser.parse_args(args)
   if not args:
     print('Current base-url:')
     return RunGit(['config', 'branch.%s.base-url' % branch],