Fix issue reported from github

Summary:
we filter the $actors above such that its possible to have no $actor anymore (if $actor is not a deliverable email address). ergo, make sure we have actor before we start calling methods.

Fixes github issue 403

Test Plan: logic on this one - not 100% sure how to easily reproduce

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7284