In PHUIInfoView, only show list UI if more than 1 item

Summary: We often just setError as an array even if it's only one error. This just makes the UI a little cleaner in these cases.

Test Plan: Remove all reviewers from a diff, see status error without list styling.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14308