[ticket/11520] Re-adjust userpost count on topic fork

PHPBB3-11520
[ticket/11520] Coding guideline compliance

PHPBB3-11520
[ticket/11520] Re-adjust userpost count on topic fork

PHPBB3-11520
Merge pull request #2833 from Geolim4/ticket/11520

[ticket/11520] Re-adjust userpost count on topic fork