Performance increasing

[dbeylkhanov]

@rasmuschristensen I think that comparison like
Items.IndexOf(item) == Items.Count - 1;

is better for two reasons:

1. with using your check - I'm stuck on first time already, when we need to get more items (in particular, in my case it's not working properly), cuz, it's starts recursively request command executing, e.g. we have 20 items, I scroll to bottom, load event is fired and we load+20 items, then it's immediately starts check current item visibility which is appeared, and then it wants to get more items again. And this continues on a continuous
2. I check index of listview item and it's faster than your way