Ponder - fix redirect after leaving a question comment

Summary: we did some security lock down on URI stuff and I think this was a casualty. Fixes T5992.

Test Plan: left a comment, got redirected. no more 500 response.

Reviewers: chad, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5992

Differential Revision: https://secure.phabricator.com/D10388