Fix avatar when commit email is an empty string

What does this MR do and why?

Fix avatar when commit email is an empty string

Render the default avatar instead of the first user with a blank public email

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create a commit with a blank email

   git commit -m "Test no email" --author "No Email <>"

2. View the commit in the web UI

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.