Handle case when you are using the os_fast pinserver path, but you are not using pin for private files.

#6493 
When:
1. You hit the os_fast/... path for a private file
2. You have disabled pin auth for private files
3. Your site is not pin protected.
4. The file exists

Then:
You should be sent to the standard drupal private file path "system/file..." in order to allow for site members to see the private file files