Display avatar if not logged in

[solkaz]

Description

Sets the avatar URL for the author of a snippet even if the user isn't logged into Github (and thus cannot use the API).

Motivation and Context

It's a bug

Checklist:

• [x] My code follows the code style of this project.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

Browsers

• [x] Chrome
• [x] Firefox
• [x] Safari
• [ ] Mobile:
• [ ] Other: