Merge pull request hackmdio#1867 from hackmdio/refactor/reuse-random-…

…filename

refactor: reuse random filename in filesystem image provider

lib/imageRouter/filesystem.js

@@ -22,8 +22,8 @@ function randomFilename () {
  */
 function pickFilename (defaultFilename) {
   let retryCounter = 5
-  let filename = defaultFilename
   const extname = path.extname(defaultFilename)
+  let filename = `${randomFilename()}${extname}`
   while (retryCounter-- > 0) {
     if (fs.existsSync(path.join(config.uploadsPath, filename))) {
       filename = `${randomFilename()}${extname}`