Fix regression on backtopage

htdocs/core/lib/functions.lib.php

@@ -561,7 +561,8 @@ function GETPOST($paramname, $check = 'alphanohtml', $method = 0, $filter = null
 
 	// Sanitizing for special parameters. There is no reason to allow the backtopage parameter to contains an external URL.
 	if ($paramname == 'backtopage') {
-		$out = preg_replace(array('!(\\\|/)+!', '/^[a-z]*:/'), '', $out);
+		$out = str_replace('\\', '/', $out);
+		$out = preg_replace(array('/^\/\/+/', '/^[a-z]*:/i'), '', $out);
 	}
 
 	// Code for search criteria persistence.