Fix access to trashed entitlement's entitleable
Summary:
Fixes fetching transaction details for transactions that refer
to deleted entitlements.
Test Plan: ./phpunit
Reviewers: #hkccp_developers, vanmeeuwen
Reviewed By: #hkccp_developers, vanmeeuwen
Subscribers: #hkccp_developers
Differential Revision: https://git.kolab.org/D2888