Fix issue when editing a project with no secondary hash tags

Summary: Fixes T5186. If a project has no secondary tags, we issue a bogus query right now.

Test Plan: Edited a project with no secondary tags.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T5186

Differential Revision: https://secure.phabricator.com/D9300