Event attachments: Adding an attendee to an existing event does not prompt to create a share link

[kesselb]

Steps to reproduce

1. Create an event (don't save!)
2. Click "More details"
3. Add an attachment
4. Click "Save"
5. Close the event
6. Open the event again
7. Add an attendee "Bob"
8. Click "Save"
9. Bob receives the invitation, but the attachment link is the internal link. Bob cannot access the file unless he has access to it through other means (e.g. it's a file from a group folder).

Expected behavior

There should be the prompt asking to create a share link.

Actual behaviour

No prompt to create the share link.