Workboards - fix broken links on pages accessed via tag

Summary: $this->id wasn't being set in this case so just set it explicitly after we finish loading the project. Fixes T5763.

Test Plan: links were broken no longer!

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5763

Differential Revision: https://secure.phabricator.com/D10108