BE: Awaiting delivery --> Missing does not change request status

1. As diku_admin on folio-snapshot
2. Navigate to an item record with the status Awaiting delivery
3. Mark that item Missing
4. Navigate to Requests app

Expected: request status changes to Open - not yet filled
Actual: request status remains Open - awaiting delivery

Notes: The same thing occurs for Awaiting pickup --> Missing (but not changing the same statuses to Withdrawn). Refinement session on 2020-06-05 said that that would also be fixed as part of this work.