Task: table shows 0 documents after reopening and accepting submission again

How to reproduce:

1. A task contains a submitted document of the participant and the submission was already accepted by the coach.
2. As a coach reopen the submission. A message shows up, that all submitted documents will be deleted. Click ok.
3. For the coach the document is removed. (For the participant the document is still shown under submission.)
4. As a coach click "collect documents" and accept the submission. The document is shown again for the coach. (The same happens, if the participant submits the document again.)

==> NOK: In the table view of all participants the column "Docs" shows 0.

==> OK: The column "Docs" shows 1.