Fix missing inline comments issue

Summary:
some inline comments are missing in the revision page. The
reason is that the inline comments got overwritten if multiple groups of
comments are modifying the same file
(https://secure.phabricator.com/diffusion/P/browse/master/src/applications/differential/view/revisioncomment/DifferentialRevisionCommentView.php;f6748bc1907d946ffe5a0957964a5eb5fe90514f$299).

Test Plan: the comments used to be missing renders now.

Reviewers: epriestley, nh

Reviewed By: epriestley

CC: hwang, aran

Differential Revision: https://secure.phabricator.com/D2135