Sort inline comments by id in case of ties

Summary: This ensures that two comments by the same author on the same line are sorted properly.

Test Plan: Before this patch, made two comments that appeared in the wrong order. With this patch, they sort correctly.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8697