"k" shortcut doesn't work on last item(#60). "k" on first item crashes app

[Slava Kim]

"Up" still works on last item. "Up" does not work on first item as expected

[Slava Kim]

gui.py, line 136:
if self.listbox.focus_position + 1 in self.walker.positions():
replace
if self.listbox.focus_position - 1 in self.walker.positions():

[Geoffrey]

Thanks for your issue!