Audit - fix issue "showing older" on some commits

Summary: Fixes T7021. When I moved around all the timeline stuff I guess I didn't find this "corner" case, which is wildly common in the post-commit review workflow that we don't use.

Test Plan: pre-patch I could reproduce the issue and post patch I could not. The reproduction case is to have a commit with inline comments and then enough subsequent comments to have a "show older" UI. clicking "show older" now works!

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7021

Differential Revision: https://secure.phabricator.com/D11479