[pvr] fix: remember the wrong selected item path if you close the channel osd

If you close the channel osd on a different group than the current playing group without switching to a channel of this group, the wrong selected item path is stored in the global variable. This fix it by setting the proper selected item of the current playing group.
sorry i've mixed the refactor of the member vars and methods with this fix. 
this is the most important change to fix the proper issue. 

if you close the osd with a different group than the playing group, the last selected item path is used instead of the selected item path of the view control. otherwise the selected item path of the view control is used.