On save/update, convert nbsp (\xc2\xa0 and \xa0) to space

dss_convert_nbsp_wp_insert_post_data.php

<?php
/**
 * Plugin Name: On save/update, convert nbsp to space
 *
 * From http://wordpress.stackexchange.com/a/168358, modified by me
 *
 * @package 'dss_convert_nbsp_wp_insert_post_data'
 */

add_filter( 'wp_insert_post_data', 'dss_convert_nbsp_wp_insert_post_data', '99', 2 );
/**
 * Converts nbsp to space
 *
 * @author soderlind
 * @version 1.0.0
 * @param   array $data    Sanitized post data.
 * @param   array $postarr Raw post data.
 * @return  array          Sanitized post data.
 */
function dss_convert_nbsp_wp_insert_post_data( $data, $postarr ) {
	$data = str_replace( "\xc2\xa0", '&nbsp;', $data ); // UTF-8 nbsp -> space
	$data = str_replace( "\xa0", '&nbsp;', $data );  // ISO-8859-1 nbsp -> space, why: http://stackoverflow.com/a/1462039.
	$data = str_replace( '&nbsp;', "\xc2\xa0", $data );
	return $data;
}