R1:af8ad58e6bb1

Probably fix notifications not being properly marked as unread

Summary: Fixes T8586. This wasn't quite right in D13320.

Test Plan: iiam

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8586

Differential Revision: https://secure.phabricator.com/D13331