Reset currentIndex of HistoryList to -1 when focused

Fixes issue where backspace hides keyboard
of history items increases.
1) Visit www.sailfishos.org
2) Search "sd" (assuming that you don't have "sd" sites in history)
3) Press backspace once to remove "d"
Merge pull request #115 from rainemak/resetCurrentIndex

Reset currentIndex of HistoryList to -1 when focused