Comments: Avoid a PHP notice in `comment_form()` if the `email` field is not set.

Follow-up to [46090].

Props mat-lipe.
Merges [46885] to the 5.3 branch.
Fixes #48943.
Built from https://develop.svn.wordpress.org/branches/5.3@46886


git-svn-id: http://core.svn.wordpress.org/branches/5.3@46686 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/comment-template.php

@@ -2433,7 +2433,7 @@ function comment_form( $args = array(), $post_id = null ) {
 	$args = array_merge( $defaults, $args );
 
 	// Remove aria-describedby from the email field if there's no associated description.
-	if ( false === strpos( $args['comment_notes_before'], 'id="email-notes"' ) ) {
+	if ( isset( $args['fields']['email'] ) && false === strpos( $args['comment_notes_before'], 'id="email-notes"' ) ) {
 		$args['fields']['email'] = str_replace(
 			' aria-describedby="email-notes"',
 			'',

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3.1-RC1-46884';
+$wp_version = '5.3.1-RC1-46886';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.