Fix fatal in commit message parser

Summary:
See D1195, which fataled this daemon.

https://secure.phabricator.com/daemon/log/2966/

Test Plan: Applied this patch to secure.phabricator.com, restarted daemon, it
picked up D1203.

Reviewers: btrahan, jungejason, mareksapota

Reviewed By: btrahan

CC: aran, btrahan, mareksapota

Differential Revision: 1204