Allow a null `id` to do a `name` lookup in `wp_set_current_user()`.

Previously, the `name` fallback was failing in the case where the current user
was 0, due to a loose comparison between 0 (the current user) and `null` (the
value that is used to trigger the `name` fallback).

Props bobbingwide.
Fixes #20845.
Built from https://develop.svn.wordpress.org/trunk@34947


git-svn-id: http://core.svn.wordpress.org/trunk@34912 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/pluggable.php

@@ -26,8 +26,14 @@ if ( !function_exists('wp_set_current_user') ) :
 function wp_set_current_user($id, $name = '') {
 	global $current_user;
 
-	if ( isset( $current_user ) && ( $current_user instanceof WP_User ) && ( $id == $current_user->ID ) )
+	// If `$id` matches the user who's already current, there's nothing to do.
+	if ( isset( $current_user )
+		&& ( $current_user instanceof WP_User )
+		&& ( $id == $current_user->ID )
+		&& ( null !== $id )
+	) {
 		return $current_user;
+	}
 
 	$current_user = new WP_User( $id, $name );
 

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34946';
+$wp_version = '4.4-alpha-34947';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.