listbox.go deselect error.

[TheSeeker]

When deselecting all items from a listbox using ctrl+click, the last item deselected remains active despite no longer being highlighted on the list. This can be demonstrated by going to https://gowut-demo.appspot.com/show and clicking the "ListBox" link on the left, then using ctrl+click to select and deselect items on the list. sum=? will always equal the last item deselected.

[icza]

Closing as fixed by gowut.dev pull request #2.