[podcasts] Use g_slices when possible
[podcasts] Use g_slices when possible

Memory slices are more efficient than mallocs.

kyoushuu/grilo-plugins,kyoushuu/grilo-plugins,jasuarez/grilo-plugins,grilofw/grilo-plugins,vrutkovs/grilo-plugins,MikePetullo/grilo-plugins,MikePetullo/grilo-plugins,MathieuDuponchelle/grilo-plugins,grilofw/grilo-plugins,jasuarez/grilo-plugins,MathieuDuponchelle/grilo-plugins,MathieuDuponchelle/grilo-plugins,MikePetullo/grilo-plugins,GNOME/grilo-plugins,vrutkovs/grilo-plugins,MathieuDuponchelle/grilo-plugins,kyoushuu/grilo-plugins,vrutkovs/grilo-plugins,vrutkovs/grilo-plugins,GNOME/grilo-plugins