Description:
------------
Running highlight_string() on a string with PHP code and an unterminated comment, produces output that doesn't have the comment. Additionally, when the string is dynamically generated from the file-content of a PHP file using file_get_contents(), a PHP warning about unterminated comments is present in the output.

Reproduce code:
---------------
echo highlight_string('<?php echo "hello"; /*comment*/ /*unterminated comment', true);

Expected result:
----------------
<code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php&nbsp;</span><span style="color: #007700">echo&nbsp;</span><span style="color: #DD0000">"hello"</span><span style="color: #007700">;&nbsp;</span><span style="color: #FF8000">/*comment*/&nbsp;</span><span style="color: #FF8000">/*unterminated comment;</span>
</span>
</code>

Actual result:
--------------
<code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php&nbsp;</span><span style="color: #007700">echo&nbsp;</span><span style="color: #DD0000">"hello"</span><span style="color: #007700">;&nbsp;</span><span style="color: #FF8000">/*comment*/&nbsp;</span>
</span>
</code>