Login and Registration: Use correct variable to display a single erro…

…r message.

When the `wp_login_errors` filter is used to add an error message followed by an instructional message, the former was not displayed and the latter was errouneously displayed twice above the login form.

This commit ensures that the error message is displayed as expected.

Follow-up to [56654].

Props mapumba.
Fixes #59983.

git-svn-id: https://develop.svn.wordpress.org/trunk@57142 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-login.php

@@ -257,17 +257,18 @@ function login_header( $title = 'Log In', $message = '', $wp_error = null ) {
 
 				$errors .= '</ul>';
 			} else {
-				$errors .= '<p>' . $error_message . '</p>';
+				$errors .= '<p>' . $error_list[0] . '</p>';
 			}
 
 			/**
 			 * Filters the error messages displayed above the login form.
 			 *
 			 * @since 2.1.0
 			 *
-			 * @param string $errors Login error message.
+			 * @param string $errors Login error messages.
 			 */
 			$errors = apply_filters( 'login_errors', $errors );
+
 			wp_admin_notice(
 				$errors,
 				array(
@@ -287,6 +288,7 @@ function login_header( $title = 'Log In', $message = '', $wp_error = null ) {
 			 * @param string $messages Login messages.
 			 */
 			$messages = apply_filters( 'login_messages', $messages );
+
 			wp_admin_notice(
 				$messages,
 				array(