Dispute.markAsCompleted doesn't handle rendering errors correctly

[orlando]

If the Dispute rendering fails, the Dispute is still marked as completed, leaving the user with a dispute that has no files and no way to recreate them.

We need to ensure we create the files correctly before completing the dispute.

Notes

https://github.com/debtcollective/dispute-tools/blob/development/models/Dispute.js#L244

Acceptance criteria

• If a dispute renderer fails, it shouldn't mark the Dispute as completed.

[orlando]

@duranmla I'll close this one. Right now if the dispute fails to generate the documents, these will be regenerated when you download it.