R1:a778151f28c1

Fix errors found by PHPStan

Test Plan: Ran `phpstan analyze -a autoload.php phabricator/src`.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, hach-que

Differential Revision: https://secure.phabricator.com/D17371