Fix an inverted condition for the "Reopen Revision" action

Summary: Ref T2543. I converted this condition the wrong way, missing a !. I'll cherry-pick this to stable.

Test Plan: No more "Reopen Revision" action available on open revisions.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T2543

Differential Revision: https://secure.phabricator.com/D18399