[pvr] fix pvr:// directory fetching

Reported at http://forum.kodi.tv/showthread.php?tid=209879 this looks like an ancient bug.

@opdenkamp please take a look, thanks.


eew, we really need to change this to using IDs instead of names. we've either had that in the past and it got changed, or I've started changing it once and never finished it.

besides that it's really a nasty thing to compare names, it leads to issues in case some user gives a group the same name (which is stupid, but possible and valid)