Fix Maniphest status change previews

Summary: See IRC. This will be obsoleted by ApplicationTransactions eventually, but fix issues with stauts change previews for now. Specifically, if you select "Reopen Task", it incorrectly previews as "x created this task" because the old state is not set correctly.

Test Plan: Selected "Reopen Task", saw a preview with the correct language.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D8094