Login and Registration: Check that action is a string in wp-login.php.

This prevents a PHP warning if an array is passed instead.

Follow-up to [1974], [6643], [6711], [41782], [58023], [58093].

Props leedxw, dilipbheda.
Fixes #63434.

git-svn-id: https://develop.svn.wordpress.org/trunk@60239 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-login.php

@@ -479,7 +479,7 @@ function wp_login_viewport_meta() {
  * Check the request and redirect or display a form based on the current action.
  */
 
-$action = isset( $_REQUEST['action'] ) ? $_REQUEST['action'] : 'login';
+$action = isset( $_REQUEST['action'] ) && is_string( $_REQUEST['action'] ) ? $_REQUEST['action'] : 'login';
 $errors = new WP_Error();
 
 if ( isset( $_GET['key'] ) ) {