Horizontal scroll in carousel (Flickity)

Question

I am trying to add horizontal scroll with mouse wheel into the Flickity image slider. The browser console shows these errors:

"Cannot set property 'x' of undefined"
"Cannot read property 'x' of undefined"

And those the behavior is pretty poor as you can see in this example of codepen.io

JavaScript:

$('.gallery').mousewheel(function(e) {
    e.preventDefault();
    var flkty = Flickity.data(this);

    if (!window.wheeling) {
        // console.log('start wheeling!');

        if(e.deltaX > 0 || e.deltaY < 0){
            flkty.next();
        } else if(e.deltaX < 0 || e.deltaY > 0){
            flkty.previous();
        }
    }

    clearTimeout(window.wheeling);
    window.wheeling = setTimeout(function() {
        // console.log('stop wheeling!');

        delete window.wheeling;

        // reset wheeldelta
        window.wheeldelta.x = 0;
        window.wheeldelta.y = 0;
    }, 50);

    window.wheeldelta.x += e.deltaFactor * e.deltaX;
    window.wheeldelta.y += e.deltaFactor * e.deltaY;
    if(window.wheeldelta.x > 500 || window.wheeldelta.y > 500 || window.wheeldelta.x < -500 || window.wheeldelta.y < -500){
        window.wheeldelta.x = 0;
        window.wheeldelta.y = 0;

        if(e.deltaX > 0 || e.deltaY < 0){
            flkty.next();
        } else if(e.deltaX < 0 || e.deltaY > 0){
            flkty.previous();
        }
    }

    // console.log(window.wheeldelta);

});

P.S: The code works on top of this JQuery plugin.