DAV: Share invitation is not removed on delete of the original shared folder

[alecpl]

Scenario:

1. User A shared a calendar folder with user B.
2. User B accepts the invitation

POST: https://demo.domain.tld/dav/notifications/user/[email protected]/7c7efcec-f2ed9e2c-8ae8a537-90b2d644.xml

3. A new calendar collection becomes available to user B.
4. User A deletes the shared calendar.

Result:

• the collection disappears from the user B calendar (good)
• the share invitation is still there (wrong) - and if I try to accept it I get 500 Internal Server Error.

So, the share invitation notification needs to be removed on folder delete. This is not mentioned in the standard, but seems obvious to me. Also, I'd expect the same to happen when I remove the whole user mailbox.