Fix filter on non writable collections

Steps to reproduce:

1. set 2 normal users Peter and Paul who belong to the members group
2. log in as Peter
3. create a collection
4. assign Read permission on this collection to Paul
5. log out
6. log in as Paul
7. navigate to a document
8. click on the "Add to a collection" button
9. try to select a collection

Observe that the "Loading ..." stays and the available collections are never displayed

Expected behavior: it should be possible to see and select a collection when clicking on the dropdown menu