Fix a crash on android and a little bug

[wachri]

• The app crashes on Android when the selectedIndex is undefined or null.
• If you tried to select [0], the key was set to null

[ikalangita]

Hello,
Thanks for this plugin.
How to show the picker from required view ? it works only from main controller js but from a required view controller it throws an error, i submitted the issue here : http://stackoverflow.com/questions/37742964/titanium-alloy-get-current-window-from-required-view

Thanks a lot for your help