Fix handling of implicit comment transaction in paste creation
Summary:
Fixes T9850. The getComment() test should be a hasComment() test, in order to discard empty comments.
Also backport a couple of future fixes which can get you into trouble if you reconfigure forms in awkward ways.
Test Plan: Created a new paste without a comment.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T9850
Differential Revision: https://secure.phabricator.com/D14571