[Mac] fix empty ListViewBackend.SelectedRows
[Mac] fix empty ListViewBackend.SelectedRows

Add test for an emty selection.

mminns/xwt,steffenWi/xwt,hamekoz/xwt,TheBrainTech/xwt,akrisiun/xwt,lytico/xwt,cra0zy/xwt,residuum/xwt,mminns/xwt,hwthomas/xwt,antmicro/xwt,directhex/xwt,iainx/xwt,mono/xwt