uniapp H5端在异步回调中无法调用chooseImage

1. uni.chooseImage 在手机浏览器中无法在异步回调中拉起；
2. 可以在异步完成后调用uni.showModal 然后在showModal的success回调中再去调用uni.chooseImage可以拉起成功。

chooseImage: async function() {  
    let that = this;  
    if (this.imageList.length === 3) {  
        let isContinue = await this.isFullImg();  
        if (!isContinue) {  
            return;  
        }  
    }  

    uni.chooseImage({  
        sourceType: sourceType[that.sourceTypeIndex],  
        sizeType: sizeType[that.sizeTypeIndex],  
        count: that.imageList.length + that.count[that.countIndex] > 3 ? 3 - that.imageList.length : that.count[that.countIndex],  
        success: (res) => {  
            that.imageList = that.imageList.concat(res.tempFilePaths);  
        },  
        fail: (err) => {  
        }  
    })  
},  
isFullImg: function() {  
    let that = this;  
    return new Promise((res) => {  
        setTimeout(function() {  
            //如果我把uni.showModal这段代码注释掉替换成 res(true); ，uni.chooseImage 就不会在手机端的浏览器中调起来  
            uni.showModal({  
                content: "已经有3张图片了,是否清空现有图片？",  
                success: (e) => {  
                    if (e.confirm) {  
                        that.imageList = [];  
                        res(true);  
                    } else {  
                        res(false)  
                    }  
                },  
                fail: () => {  
                    res(false)  
                }  
            })  
        },2000)  
    })  
}