worker crash on invalid docset

[adamhooper]

Seen this in a user's database. Haven't reproduced on production, dev or test:

overview-worker_1                | 2020-09-04T20:36:19.146880409Z ERROR c.o.UnhandledMessageHandler - Unhandled message from Actor[akka://worker/user/DocumentSetCommandWorker#-1788023054] to Actor[akka://worker/user/DocumentSetCommandWorker#-1788023054]: {}
overview-worker_1                | 2020-09-04T20:36:19.146900078Z com.overviewdocs.database.exceptions.package$ParentMissing: org.postgresql.util.PSQLException: ERROR: update or delete on table "file2" violates foreign key constraint "document_processing_error_file2
_id_fkey" on table "document_processing_error"
overview-worker_1                | 2020-09-04T20:36:19.146905750Z   Detail: Key (id)=(20241) is still referenced from table "document_processing_error".