R1:27b7ba814a5a

Don't consider empty inlines when considering whether a revision has draft comments or not

Summary: Ref T13513. When computing whether a revision has draft comments or not, ignore empty inlines.

Test Plan: Added empty inlines to a revision, no longer saw a yellow "draft" bubble in the list UI.

Maniphest Tasks: T13513

Differential Revision: https://secure.phabricator.com/D21215