前端通过wx.uploadImg上传图片，服务端通过调用https://api.weixin.qq.com/cgi-bin/material/get_material接口下载图片，无法下载，是什么情况？ 这是其中一次下载下来的字节： [123, 34, 101, 114, 114, 99, 111, 100, 101, 34, 58, 52, 56, 48, 48, 49, 44, 34, 101, 114, 114, 109, 115, 103, 34, 58, 34, 97, 112, 105, 32, 117, 110, 97, 117, 116, 104, 111, 114, 105, 122, 101, 100, 32, 114, 105, 100, 58, 32, 54, 54, 57, 55, 55, 97, 50, 98, 45, 49, 57, 53, 56, 51, 101, 53, 101, 45, 55, 56, 99, 102, 56, 55, 54, 99, 34, 125]