Error work on mobile devices

[lydie88]

wScratchPad.js:318 Uncaught TypeError: Cannot read property 'screenX' of undefined
at HTMLCanvasElement. (wScratchPad.js:318)
at HTMLCanvasElement.dispatch (jquery.1.11.0.min.js:3)
at HTMLCanvasElement.r.handle (jquery.1.11.0.min.js:3)

This is due to the touchend event not getting a touch object.

I've modified my wScratchPad.js L:288
and replaced $.fn.bindMobileEvents function with below.

  $.fn.bindMobileEvents = function () {
    var touchScreenX = 0.0
    var touchScreenY = 0.0
    var touchClientX = 0.0
    var touchClientY = 0.0
    var target = null;
  
    $(this).on('touchstart touchmove touchend touchcancel', function (event) {
      var touches = (event.changedTouches || event.originalEvent.targetTouches),
          first = touches[0],
          type = '';

      switch (event.type) {
      case 'touchstart':
        type = 'mousedown';
        break;
      case 'touchmove':
        type = 'mousemove';
        event.preventDefault();
        break;
      case 'touchend':
        type = 'mouseup';
        break;
      default:
        return;
      }
      
      if ( first ) {
        touchScreenX = first.screenX;
        touchScreenY = first.screenY;
        touchClientX = first.clientX;
        touchClientY = first.clientY;
        target = first.target;
      }

      var simulatedEvent = document.createEvent('MouseEvent'); 

      simulatedEvent.initMouseEvent(
        type, true, true, window, 1, 
        touchScreenX, touchScreenY, touchClientX, touchClientY, 
        false, false, false, false, 0/*left*/, null
      );

      target.dispatchEvent(simulatedEvent);
    });

Simply caching the parameters solves the issue, but this isn't a permanent solution.