Gracefully handle cases where the revision was comandeered

[tomrittervg]

This is super rare, but it shouldn't be difficult to handle.

abandon got back the error

Got an error from phabricator when trying to abandon 260609: {'error': 'ERR-CONDUIT-CORE', 'errorMessage': 'ERR-CONDUIT-CORE: <differential.revision.edit> Validation errors:\n - You can not abandon this revision because you are not the author. You can only abandon revisions you own. You can change this behavior by adjusting the "differential.always-allow-abandon" setting in Config.', 'response': None}