Fix double escaping in phutil_tag
Summary:
I wasn't able to reproduce the "recursion detected" in real web request but I saw lots of 1073741824 refcounts in debug_zval_dump() of $object.
I'm not sure how that happens.
Test Plan: D4807#4
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T2432
Differential Revision: https://secure.phabricator.com/D4839