Allow append on empty item list.
Allow append on empty item list.

If you initialise a simple RecycleView with data = [], it will die on the first item append because computed_positions list is empty. Changing so an empty list append is processed like setting a new list.

kivy/kivy,matham/kivy,jegger/kivy,darkopevec/kivy,inclement/kivy,LogicalDash/kivy,bionoid/kivy,rnixx/kivy,bionoid/kivy,jkankiewicz/kivy,kived/kivy,tony/kivy,jkankiewicz/kivy,rafalo1333/kivy,Cheaterman/kivy,janssen/kivy,kived/kivy,tony/kivy,inclement/kivy,LogicalDash/kivy,manthansharma/kivy,el-ethan/kivy,KeyWeeUsr/kivy,jkankiewicz/kivy,el-ethan/kivy,manthansharma/kivy,jegger/kivy,jegger/kivy,bionoid/kivy,andnovar/kivy,akshayaurora/kivy,darkopevec/kivy,autosportlabs/kivy,LogicalDash/kivy,KeyWeeUsr/kivy,bionoid/kivy,kived/kivy,manthansharma/kivy,tony/kivy,kivy/kivy,janssen/kivy,matham/kivy,janssen/kivy,aron-bordin/kivy,aron-bordin/kivy,rafalo1333/kivy,kivy/kivy,rnixx/kivy,KeyWeeUsr/kivy,LogicalDash/kivy,janssen/kivy,akshayaurora/kivy,akshayaurora/kivy,autosportlabs/kivy,aron-bordin/kivy,manthansharma/kivy,Cheaterman/kivy,jkankiewicz/kivy,KeyWeeUsr/kivy,inclement/kivy,autosportlabs/kivy,matham/kivy,andnovar/kivy,darkopevec/kivy,darkopevec/kivy,rafalo1333/kivy,Cheaterman/kivy,Cheaterman/kivy,aron-bordin/kivy,andnovar/kivy,jegger/kivy,el-ethan/kivy,rnixx/kivy,matham/kivy