uni.downloadFile 搭配uni.saveFile下载文件，下载的文件没有后缀名无法打开，文件名也不对

比如下载下面URL的图片，下载到手机里的文件变成了“fileDownload”，并且没有后缀名

getDownload() {  
                    const downloadTask = uni.downloadFile({  
                        url: 'http://10.4.120.78:8802/service/sys/fileDownload?localPath=cmecFiles/merge&fileName=8bc46b3880fb5a1c6eb9bf61a71c646e-icon-52.png',   
                        success: (res) => {  
                            if (res.statusCode === 200) {  
                                console.log('下载成功',res);  
                            }  
                            let that = this;  
                            uni.saveFile({  
                                tempFilePath: res.tempFilePath,  
                                    success: function(red) {  
                                        that.luj = red.savedFilePath  
                                        console.log(red,'保存成功')  
                                        uni.showToast({  
                                            icon: 'none',  
                                            mask: true,  
                                            title: '文件已保存：' + red.savedFilePath, //保存路径  
                                            duration: 3000,  
                                        });  
                                        setTimeout(() => {  
                                            //打开文档查看  
                                            uni.openDocument({  
                                                filePath: red.savedFilePath,  
                                                success: function(res1) {  
                                                    console.log(res1,'打开文档成功');  
                                                }  
                                            });  
                                        }, 3000)  
                                    }  
                                });  
                            }  
                        });  

                        downloadTask.onProgressUpdate((res) => {  
                            console.log('下载进度' + res.progress);  
                            console.log('已经下载的数据长度' + res.totalBytesWritten);  
                            console.log('预期需要下载的数据总长度' + res.totalBytesExpectedToWrite);  
                    });  
                },