zoompic插件中通过对图片双击或双指放大，在控制台报错

iSlider.plugin.zoompic.js?9af6:285 Uncaught TypeError: Cannot read property 'pageX' of undefined
at handleDoubleTap (iSlider.plugin.zoompic.js?9af6:285)
at iSlider.endHandler (iSlider.plugin.zoompic.js?9af6:314)
at iSliderPrototype.handleEvent (iSlider.js?c3de:1183)

这一段代码
/**
* Double tao handle
* @param {object} evt
*/
function handleDoubleTap(evt) {
var zoomFactor = zoomFactor || 2;
var node = zoomNode;
var pos = getPosition(node);
currentScale = currentScale == 1 ? zoomFactor : 1;
node.style.webkitTransform = generateTranslate(0, 0, 0, currentScale);
if (currentScale != 1) node.style.webkitTransformOrigin = generateTransformOrigin(evt.touches[0].pageX - pos.left, evt.touches[0].pageY - pos.top);
}

pageX报错

Start in iSlider.plugin.zoompic.js at handleDoubleTap around line 285, then trace the call from iSlider.endHandler and handleEvent. Reproduce the double-tap and pinch-to-zoom actions and inspect the event data reaching the handler. Done means both interactions no longer report the pageX TypeError in the console.

Written by the indexing model from the issue text.