Return 404 instead of 500 when an "original parent" has been deleted

[kjac]

Prerequisites

• I have added steps to test this contribution in the description below

Description

The API explicitly returns a 500 response code if the "original parent" of a "restore from recycle bin" attempt is not found:

This seems very dramatic 😄 specially since this is a normal, expected scenario; the "original parent" has simply been deleted from the recycle bin, before the attempt to restore the previous child is made.

This PR changes the response code to be a 404 instead. Less dramatic 😛

Testing this PR

1. Create a parent and a child document.
2. Move the child to the recycle bin.
3. Delete the parent entirely.
4. Request the "original parent" from /umbraco/management/api/v1/recycle-bin/document/{key}/original-parent.
5. Verify that a 404 is returned.

Rinse and repeat for media.

Note that "move to recycle bin" and "delete" operations are currently only functional through the API (in other words, use Swagger).

[Migaroez]

It took me a while to follow your train of thought, but you are right. There is a reasonable course where the relation would not exists (cleanup of relation because parent was fully deleted).