Bootstrap/Load: Fix bug causing AJAX functions to return a 500 when passing a null response to wp_die().

This bug was introduced in [44497].

Props ocean90.
See #45933.

Built from https://develop.svn.wordpress.org/trunk@44673


git-svn-id: http://core.svn.wordpress.org/trunk@44504 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -3293,7 +3293,8 @@ function _ajax_wp_die_handler( $message, $title = '', $args = array() ) {
 
 	list( $message, $title, $r ) = _wp_die_process_input( $message, $title, $args );
 
-	if ( ! headers_sent() && null !== $r['response'] ) {
+	// This is intentional. For backward-compatibility, support passing null here.
+	if ( ! headers_sent() && null !== $args['response'] ) {
 		status_header( $r['response'] );
 	}