Add missing `case` for personal ruls which create blocking reviewers

Summary: Ref T1279. I only tested the global case. :O

Test Plan: Created a personal "add me as blocking" rule.

Reviewers: btrahan, zeeg

Reviewed By: zeeg

CC: aran

Maniphest Tasks: T1279

Differential Revision: https://secure.phabricator.com/D7261