Fix broken handle rendering in Ponder

Summary: Ref T5817. This just fixes the markup in emails, the overall behavior still isn't great. I don't want to spend to much time on Ponder until it ends up somewhere nearer the top of the priority queue.

Test Plan: Viewed feed stories and emails, no stray/clearly-broken HTML.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5817

Differential Revision: https://secure.phabricator.com/D10231