解决js error "TypeError: null is not an object (evaluating 's.onComplete')"

[maqianqiandegithup]

https://github.com/airbnb/lottie-web/blob/master/player/js/utils/DataManager.js#L619
上面折行代码中， 检测到process.onComplete 执行时偶发js error "TypeError: null is not an object (evaluating 's.onComplete')"，希望这行代码执行前能够对process进行判空，对process.onComplete和process.onError进行有效判断