Project avatar not loaded for custom server instance
### Summary
For custom gitlab server instances I can't download project avatar but for user it works.
### Steps to reproduce
It works:
```bash
curl -X GET -H "Host: my_gitlab.com" -H "Connection: Keep-Alive" -H "Accept-Encoding: gzip" -H "User-Agent: okhttp/3.11.0" -H "PRIVATE-TOKEN: my_private_token" --compressed "https://my_gitlab.com/api/v4/users/938"
Warning: Binary output can mess up your terminal. Use "--output -" to tell
Warning: curl to output it to your terminal anyway, or consider "--output
Warning: <FILE>" to save to a file.
```
It doesn't work:
```bash
curl -X GET -H "User-Agent: Dalvik/2.1.0 (Linux; U; Android 8.1.0; Mi A1 MIUI/V9.6.8.0.ODHMIFE)" -H "Host: my_gitlab.com" -H "Connection: Keep-Alive" -H "Accept-Encoding: gzip" -H "PRIVATE-TOKEN: my_private_token" --compressed "https://my_gitlab.com/uploads/-/system/project/avatar/947/l-icon.png"
<html><body>You are being <a href="https://my_gitlab.com/users/sign_in">redirected</a>.</body></html>
```
issue