Fix credential upgrade issue after introduction of isLocked column

Summary: Fixes T5035. This migration isn't forward compatible after schema mutation.

Test Plan: Ran locally, will get reporting user to confirm.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: gera, epriestley

Maniphest Tasks: T5035

Differential Revision: https://secure.phabricator.com/D9101