fix: 回退 uni.saveFile 文件命名规则，避免存在特殊符号导致的部分问题

src/platforms/app-plus/service/api/file/file.js

 import {
   warpPlusMethod,
   warpPlusErrorCallback,
-  getFileName
+  getExtName
 } from '../util'
 
 import {
@@ -25,8 +25,7 @@ export function saveFile ({
   tempFilePath
 } = {}, callbackId) {
   const errorCallback = warpPlusErrorCallback(callbackId, 'saveFile')
-  let fileName = getFileName(tempFilePath)
-  fileName = `${Date.now()}${index++}_${fileName}`
+  const fileName = `${Date.now()}${index++}${getExtName(tempFilePath)}`
 
   plus.io.resolveLocalFileSystemURL(tempFilePath, entry => { // 读取临时文件 FileEntry
     getSavedFileDir(dir => {

src/platforms/app-plus/service/api/util.js

@@ -206,3 +206,8 @@ export function getFileName (path) {
   const array = path.split('/')
   return array[array.length - 1]
 }
+
+export function getExtName (path) {
+  const array = path.split('.')
+  return array.length > 1 ? '.' + array[array.length - 1] : ''
+}