(stable) Always show "X requested review" in mail to stop some undraft mail from being dropped

Summary: Ref T13035. See that task for a description of the issue.

Test Plan:

• Enabled prototypes.
• Disabled all Herald rules that trigger Harbormaster builds.
• Created a new revision.
• Before patch: initial review request email was dropped.
• After patch: initial review request email is sent.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13035

Differential Revision: https://secure.phabricator.com/D18851