R1:bbc2ae78589b

Fix task graph fatal for graphs containing restricted tasks

Summary: Fixes T11392. If some tasks are restricted, we only have PHIDs for them, not objects. Just use the PHIDs instead.

Test Plan: {F1741335}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11392

Differential Revision: https://secure.phabricator.com/D16345