User::actkey is always a string
Summary:
This fixes the following issue:
PHP Fatal error: Uncaught TypeError:
Cannot assign null to property User::$actkey of type string
in /var/51-wwwroot/zed/includes/objects/user.php:125
Fixes T118#630.
Test Plan: Test on zed51.
Reviewers: dereckson
Reviewed By: dereckson
Maniphest Tasks: T118
Differential Revision: https://code.zed.dereckson.be/D28