Check policy.locked slightly sooner in PhabricatorApplication

Summary: We could still miss this if the policy had never been customized and we returned early after one of the other checks.

Test Plan:
Works great on instances now.

{F267067}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11374