MWEB-1066 Fix PHP fatal error on production

After [type hinting changes](https://github.com/Wikia/app/commit/3c90277780b70f14b2c190a1e8d8f8c57878b422#diff-8812c5dca1cb67ed8d0d9f3c9bfa3cbdR53) in `ApiHooks.class.php` users are not able to remove nested comments anymore. That's because a catchable fatal error occurs while trying to remove the comment with sub-comments.

The changes in this pull request fix it.

/cc @Grunny @macbre @idradm