[ticket/13138] Do not use cookie data and autologin while forcing a user_id

PHPBB3-13138
Merge pull request #3039 from nickvergessen/ticket/13138

[ticket/13138] Only use cookie data when we do not force a user_id
Merge branch 'develop-olympus' into develop-ascraeus

* develop-olympus:
  [ticket/13138] Do not use cookie data and autologin while forcing a user_id

Conflicts:
	phpBB/phpbb/session.php