The string 'USER.' as a role value breaks the Announcements display portlet

The Announcements portlet supports roles:  admin, moderator, author, and audience.

Mostly we add portal groups to these roles, but you can add individual users as well.  When you do, it stores a string like 'USER.rsmith' in the corresponding database column.

If the username part ('rsmith' above) is missing, it breaks the display portlet for anyone who receives the corresponding Topic.