wx.cloud.downloadfile 的临时文件下载不了

wx.cloud.downloadfile 下使用wx.saveImageToPhotosAlbum 保存的图片怎么是xml格式的

downloadPhoto: function(e) {     wx.cloud.downloadFile({       fileID: this.data.photo,     }).then(res => {       wx.saveImageToPhotosAlbum({         filePath: res.tempFilePath,         success: res => {           wx.showToast({             title: '下载成功',           })         },         fail: err => {           console.error(err)         }       })     }).catch(error => {       // handle error     })   },