'update_meta_cache()' doesn't correctly handle the return value of the 'update_{$meta_type}_metadata_cache' filter

[donglijun]

The return type of update_meta_cache() is array or false, but the return value of update_{$meta_type}_metadata_cache filter is forcibly cast to bool and returned in update_meta_cache().
wp-includes/meta.php: 1149

        $check = apply_filters( "update_{$meta_type}_metadata_cache", null, $object_ids );
        if ( null !== $check ) {
                return (bool) $check;
        }

This may cause get_metadata_raw() to produce incorrect results.
wp-includes/meta.php: 646

        if ( ! $meta_cache ) {
                $meta_cache = update_meta_cache( $meta_type, array( $object_id ) );
                if ( isset( $meta_cache[ $object_id ] ) ) {
                        $meta_cache = $meta_cache[ $object_id ];
                } else {
                        $meta_cache = null;
                }
        }