R1:c98be54bf4e6

Don't show tag when no topic is set

Summary: Check the strlen of topic before adding a tag to the header in Conpherence.

Test Plan: Remove a topic, no longer see indigo bubble.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17715