[pvr] fix internal group loading

As we never load the internal groups from our TV database, changing the group name in our group manager has no effect. This fixes the loading of the internal channel groups.

Furthermore I'm currently working on the feature to hide different channel groups and determined that my changes to the internal groups within the database are never reflected in the code. That would be the next issue if we don't fix it now.

@opdenkamp for review would be much appreciated ;)