Move revisions without reviewers to author's queue

Summary:
If the revision doesn't have reviewers then it's really not waiting on someone else and the author must take an action.
An improvement would be to check if the reviewers are not disabled but that would require loading their handles.

Test Plan:
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/differential/

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin, s.o.butler

Differential Revision: https://secure.phabricator.com/D5046