When a user is a member of no projects, show them no triage tasks, not all triage tasks

Summary: The "with projects ... " query boils down to "all triage tasks" when
you don't belong to any projects. Just render the "no needs triage in projects
you are a member of" element unconditionally in this case.

Test Plan: Looked at homepage as a user with no project memberships but some
triage-requiring tasks before and after this change. Prior to this change, all
triage tasks show; afterwards, none.

Reviewers: fratrik, btrahan

Reviewed By: fratrik

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1620