User and group names aren't displayed correctly for guests in an app's livetable

Steps to reproduce:

1. Create an app using App Within Minutes
2. In the second step add 2 fields: an user picker and a group picker
3. In the third step add these 2 fields as columns for the livetable
4. Add a new entry and select Admin for the user picker and XWikiAdminGroup for the group picker
5. Go back to the app's homepage and log-out