fix: use randomFileName as default start file name to ensure the randomness

Signed-off-by: Yukai Huang <yukaihuangtw@gmail.com>

Author: Yukaii

lib/imageRouter/filesystem.js

@@ -22,7 +22,7 @@ function randomFilename () {
  */
 function pickFilename (defaultFilename) {
   let retryCounter = 5
-  let filename = defaultFilename
+  let filename = randomFilename()
   const extname = path.extname(defaultFilename)
   while (retryCounter-- > 0) {
     if (fs.existsSync(path.join(config.uploadsPath, filename))) {