Patch 'drag to outside window' bug

Noticed a bug when I dragged from the middle of the bar to outside the window.

1.  Uncaught TypeError: Cannot read property '0' of undefined rangeslider.min.js:2
At: b.originalEvent.touches[0]
Fix: (b.originalEvent.touches && b.originalEvent.touches[0])

Did the similar fix for e.currentPoint.x and then added a fallback to 0 at the end in case none of them worked.