Users: `wp_signon()` expects an array as the `$credentials` argument, not a string.

If an empty string was passed, redeclare it as an empty array to avoid a warning and a fatal error in PHP 7.1.0 Alpha 1.

Props simonvik.
Fixes #37071.
Built from https://develop.svn.wordpress.org/trunk@37697


git-svn-id: http://core.svn.wordpress.org/trunk@37663 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/user.php

@@ -27,6 +27,8 @@
  */
 function wp_signon( $credentials = array(), $secure_cookie = '' ) {
 	if ( empty($credentials) ) {
+		$credentials = array(); // Back-compat for plugins passing an empty string.
+
 		if ( ! empty($_POST['log']) )
 			$credentials['user_login'] = $_POST['log'];
 		if ( ! empty($_POST['pwd']) )

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.6-alpha-37696';
+$wp_version = '4.6-alpha-37697';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-login.php

@@ -790,7 +790,7 @@ default:
 
 	$reauth = empty($_REQUEST['reauth']) ? false : true;
 
-	$user = wp_signon( '', $secure_cookie );
+	$user = wp_signon( array(), $secure_cookie );
 
 	if ( empty( $_COOKIE[ LOGGED_IN_COOKIE ] ) ) {
 		if ( headers_sent() ) {