Fix an issue with attempting to index comments on packages
Summary: See rPcd14194a329788d5fff6365bcade278fd18f3612 for a similar change. Implement getApplicationTransactionCommentObject() to return null explicitly.
Test Plan: Ran bin/search index --type ownerspackage, got indexing after change.
Reviewers: amckinley
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D18715