Don't show a blank line if there is no user data
SKIP lines, for instance, often have no UserData; there is no
reason to display a content-less blank line.
Test Plan: arc unit
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D18632