Fix object extraction from user profile blurbs

Summary: Fixes T10242. Currently, we don't extract files, mentions, etc., properly from user profile blurbs.

Test Plan: Uploaded a file to my profile blurb, saw it attach properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10242

Differential Revision: https://secure.phabricator.com/D15153