Check for strlen instead of null for Maniphest title

Summary: Fixes T12744. Unclear why null doesn't work here but does for the title, but !strlen seems to work fine in both cases.

Test Plan: Create a new task, check mail folder, see [Created]

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12744

Differential Revision: https://secure.phabricator.com/D18002