Diff avatar improvements
What does this MR do?
Fixes a few issues with the diff comment avatars.
On merge request commit pages it would render the avatar container incorrectly which caused the comment button to be pushed out way too far to the left.
After commenting on a commit line it was then possible to throw a JS error on the discussion tab by trying to comment on this discussion. We don't show the avatars on the discussion tab so it was incorrectly trying to render this. This same error (with the class being on the element incorrectly) also caused an error to happen with not only the avatar being displayed, but it also being possible to destroy the form.