Fix a bug with owners analysis of commits

Summary: If the commit has a known author but that author is different from the revision author or the revision doesn't exist, we'll throw away the commit author and then raise an audit for "Owners Not Involved". Instead, we should just use the commit author in all cases.

Test Plan:
Debugged this with Zor in IRC, he reported it fixed his issue.

Before:

http://pastie.org/4574680

("Author" is empty.)

After:

http://pastie.org/4574712

("Author" is correctly recognized.)

Reviewers: jungejason, nh, vrana, btrahan

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D3374