Question bank: "share with pool" dialog shows too much

How to reproduce:

1. a user is assigned to some pools (public shares)
2. in the question pool, choose a question from "my questions"
3. click the button "share" and choose "share with pool"
4. NOK: the dialog shows all shared pools, even if they are not public or the user is not assigned to them (see screenshot)
5. OK: the sharing dialog should only show public pools and pools, the user is assigned to