Multisite: Remove an unnecessary if clause wrapping the `added_existing_user` filter.

This was accidentally introduced in [41125]. Since the `added_existing_user` filter has historically accepted either `true` or a `WP_Error` object, the clause is not necessary here. The doc block has been adjusted to account for the new possible `WP_Error` condition.

Fixes #41101.

Built from https://develop.svn.wordpress.org/trunk@41324


git-svn-id: http://core.svn.wordpress.org/trunk@41155 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/ms-functions.php

@@ -2110,17 +2110,16 @@ function add_existing_user_to_blog( $details = false ) {
 		$blog_id = get_current_blog_id();
 		$result = add_user_to_blog( $blog_id, $details[ 'user_id' ], $details[ 'role' ] );
 
-		if ( ! is_wp_error( $result ) ) {
-			/**
-			 * Fires immediately after an existing user is added to a site.
-			 *
-			 * @since MU (3.0.0)
-			 *
-			 * @param int   $user_id User ID.
-			 * @param mixed $result  True on success or a WP_Error object if the user doesn't exist.
-			 */
-			do_action( 'added_existing_user', $details['user_id'], $result );
-		}
+		/**
+		 * Fires immediately after an existing user is added to a site.
+		 *
+		 * @since MU (3.0.0)
+		 *
+		 * @param int   $user_id User ID.
+		 * @param mixed $result  True on success or a WP_Error object if the user doesn't exist
+		 *                       or could not be added.
+		 */
+		do_action( 'added_existing_user', $details['user_id'], $result );
 
 		return $result;
 	}

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-alpha-41323';
+$wp_version = '4.9-alpha-41324';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.