Getting HTTP 302 -> /403 on displaying uploaded images after answer "update"

## Describe the bug

Not sure when it started (maybe with 1.2.1 or after running 1.2.1 for some days, but not sure), and have no idea how to analyze the following issue:

Uploading images works well, they're written to the `updates` folder in the file system.
But when displaying them, answer returns a HTTP 302 redirecting to `/403`.

Uploaded avatars and the brand image are still working.

There are no additional information in debug log, pardon me, I've no idea how to taggle this.

The installation is private, when changing it to public, images are shown. so it seems to be related to login session handling for images downloads.

### To Reproduce

Steps to reproduce the behavior:

1. having a private answer
1. deploy a rebuild answer binary (`answer build --with-plugins...`)
1. uploaded images result int http 302 -> /403 
1. clear cookie `visit` and reload page
1. uploaded images work again

### Expected behavior

Uploaded images continue to being shown also after answer updates

### Screenshots

If applicable, add screenshots or video to help explain your problem.

### Platform

- Device: Any
- OS: Official answer container image
- Version: v1.2.1 `--with-plugins`

Non viene indicato alcun file sorgente né alcun test. Riproduci il problema su un’installazione privata ricompilando il binario Answer, quindi esamina il percorso di download delle immagini e la gestione della sessione di accesso; il lavoro è completato quando le immagini caricate rimangono accessibili dopo un aggiornamento senza cancellare la visit cookie.

Scritto dal modello di indicizzazione a partire dal testo della issue.