R1:3de002c8414a

Fix a commit hook issue where pushing dangerous changes would fatal before hitting the dragon bureaucrats

Summary: See <https://discourse.phabricator-community.org/t/php-fatal-when-using-git-push-d/1317>. The behavioral changes for Herald on initial import from D19265 could leave `$all_updates` undefined if we throw early enough.

Test Plan: Pushed a dangerous change, saw dragon bureaucrats again.

Differential Revision: https://secure.phabricator.com/D19297