Always show build target tabs, even if they have no data
Summary:
Ref T8096. Hit this on IRC:
epriestley: what's in the Messages tab?
jdoe: what Messages tab??!
epriestley: ughhhh
Test Plan: Clicked "Messages" tab, saw helpful "no messages" message.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T8096
Differential Revision: https://secure.phabricator.com/D13846