User with no workspace is stuck while logging in

Created by: piotrgrubicki

1. Create w contributor user.
2. Assign it to a workspace.
3. Delete this workspace.
4. Try to log in as this user.

Current result: The workspaces endpoint returns 500, and the UI finally shows "Internal server error" and "Go back home", which has not use whatsoever because it just repeats the sequence. No way to log out.

Expected result: A message about not being assigned to any workspace and a button to log out.