R1:d9a04fcb5342

Minor, make sure we release locks in pull daemon if we fail in unusual ways

Summary: A user is reporting a re-lock in this daemon, which I can't
reproduce, but might be possible if this throws. Stop it from throwing in
a way which evades unlock.

See: <https://github.com/facebook/phabricator/issues/476>

Auditors: btrahan