Fix avatar collision on profile, post and edit screens

[katag9k]

Description

Fixes filtering issues when a user has the same id as a guest-author post id on the post list screen, profile screen and the post edit takeover pop-up.

Related: #960 #973 #974

Steps to Test

Create a guest user that has the same post_id as another WP user_id.

In one browser, log in as the WordPress user and edit a post. In another browser login as the guest user. While logged in as a guest user, go to the post list at /wp-admin/edit.php the post will be locked as it's being edited by the WordPress user, however, the incorrect guest user's gravatar will be displayed.

Correct avatar should be:

Click edit on the post that is being edited, the warning popup will also have the incorrect gravatar from the guest user.

Correct avatar should be:

Take over the post editing. Go back to the browser where the Guest User was editing the post and wait for the "Somone else has taken over this post" pop-up. The incorrect avatar will be displayed:

The correct avatar should be:

Now log in as the WordPress user and go to the profile page at /wp-admin/profile.php the incorrect gravatar is displayed.

The correct avatar for the WordPress user:

[BrookeDot]

@katag9k, @GaryJones after some more testing it appears that this PR may be missing the condition when the post lock is removed via JS/Ajax. Adding the following appears to resolve it, but the two conditionals could likely be combined.

Thoughts?

// Do not filter the avatar if this is doing a heartbeat request on WP refresh lock
        if ( wp_doing_ajax() && isset( $_POST['action'] ) && $_POST['action'] === 'heartbeat' ) {
            return $args;
        }

[GaryJones]

@katag9k The merge conflict will need addressing please, as well as considering Brooke's comment.

[katag9k]

@BrookeDot Thank you, PR updated with the suggested code.

@GaryJones We are conflict free.