[pvr] fix loop in CGUIWindowPVRChannels::SelectNextGroup
[epg] fixed possible crash in CGUIEPGGridContainer::Render(). credits to forum user 'x-cimo'
... and fixed the typo in d108eaf9f9aa2cdf079f7edda2f087c966be7e8d
[pvr] work around for frodo to fix CPVRDatabase::RemoveStaleChannelsFromGroup for both sqlite3 and mysql