[ticket/12401] Add $topic_data array to core.viewtopic_modify_post_row event

$topic_data array is used in viewtopic.php to populate $post_row template
block array data. Although $topic_data is not being passed
to core.viewtopic_modify_post_row event for modifying/adding
$post_row data in it. So, pass this array to the event.

<a href="https://tracker.phpbb.com/browse/PHPBB3-12401">PHPBB3-12401</a>.