Use ManiphestTaskQuery instead of ad-hoc load in Maniphest reports

Summary: Fixes T5829. This stuff is old and busted, but keep it working for now.

Test Plan: No more fatal when there are recently closed tasks.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5829

Differential Revision: https://secure.phabricator.com/D10201