[ticket/13326] add viewtopic_url to event

https://tracker.phpbb.com/browse/PHPBB3-13326

PHPBB3-13326
[ticket/13326] fix CS

https://tracker.phpbb.com/browse/PHPBB3-13326

PHPBB3-13326
Merge pull request #3130 from omniError/ticket/13326

[ticket/13326] add viewtopic_url to event