Render ApplicationSearch errors correctly

Summary:
Fixes T8774. When an ApplicationSearch page returned an error (e.g., using a "viewer()" query while logged out), we would try to add action links to a box without a header. Instead:

• If a box has no header, but has show/hide actions, just create an empty header so the view renders. This is a little silly looking but does what the caller asks.
• Always set the title on the result box, so we get a header.

Test Plan: Did an invalid (logged out, with viewer()) search. Did a valid search.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T8774

Differential Revision: https://secure.phabricator.com/D13576