Description:
------------
When I use highlight_string() on unclosed /* comment it doesn't returns anything, after this comment.

Reproduce code:
---------------
highlight_string('<?php /*some comment..');
highlight_string('<?php 
some code
some code
some code
/* some comment..');

Expected result:
----------------
In first example it should return:
<?php /*some comment..
In second:
<?php 
some code
some code
some code
/* some comment..

Actual result:
--------------
In first example it returns:
<?php
In second it returns:
<?php 
some code
some code
some code