Fix edits of Ponder comments which mention other objects

Summary: Fixes T9806. See some discussion there.

Test Plan:

• Edited a comment with T12 in it.
• Before change: exception.
• After change: no exception.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9806

Differential Revision: https://secure.phabricator.com/D14539