Livechat agent's avatar is not shown when unauthenticated avatar access is blocked.

Description

When public access to avatars is blocked (as according to the log is going to be the default soon, livechat agents have no avatars). Perhaps there could be a regular profile avatar to which access is blocked, and a secondary avatar for livechat agent activity to which public access is granted?

Steps to reproduce

1. Go to Adminstration, Accounts, Avatar. Toggle "Block Unauthenticated Access to Avatars".
2. If it's on, the livechat agent's avatar appears as a black square, else it is visible. Make sure to clean your browsers cache, or else the picture might still be visible after toggling on blocking.
3. Check the log. It reads "The server detected an unauthenticated access to an user avatar. This type of request will soon be blocked by default."

Expected behavior

The following sections must not be removed, or else the BOT will close it immediately again:

Actual behavior

The following sections must not be removed, or else the BOT will close it immediately again:

Server Setup Information

The following sections must not be removed, or else the BOT will close it immediately again:

Version of Rocket.Chat Server

3.3.0

No files or tests are named. Reproduce the issue from Administration > Accounts > Avatar with unauthenticated avatar access blocked, then trace the livechat agent avatar entry point and the access-denial log. Done means the agent avatar displays under the blocked setting without causing an unauthenticated avatar access warning.