Only reset auth_key on error -404
Only reset auth_key on error -404

This error is "auth key not found", and the authorization key should
probably not be reset on other error codes. This might address #1457.

LonamiWebs/Telethon,LonamiWebs/Telethon,LonamiWebs/Telethon,LonamiWebs/Telethon