Slightly improve behavior for unverified + unapproved users

Summary: Ref T4140. Allow unapproved users to verify their email addresses. Currently, unapproved blocks email verification, but should not.

Test Plan: Clicked email verification link as an unapproved user, got email verified.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T4140

Differential Revision: https://secure.phabricator.com/D7618