Fix "Show More Messages" bug in Conpherence

Summary: Hides the search form itself as well when not in use.

Test Plan: Write lots of posts, scroll up to "see more messages", see I can click and load messages now.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16706