[ticket/13234] Never allow autologin/remember me to modify the userid

This prevents admin relogin with forced user id from overwriting
remember me cookies

PHPBB3-13234
Merge branch 'ticket/13234' into ticket/13234-2

* ticket/13234:
  [ticket/13234] Never allow autologin/remember me to modify the userid
[ticket/13234-2] Never allow autologin/remember me to modify the userid

Ascraeus version of 64d97d0787a63b3c646f89237574ac566ed89c50 commit

PHPBB3-13234
[ticket/13234-2] Correctly verify that user_id is set in user data array

PHPBB3-13234-2
[ticket/13234] Fix conditions and CS

PHPBB3-13234
Merge branch 'ticket/13234' into ticket/13234-2

* ticket/13234:
  [ticket/13234] Fix conditions and CS

Conflicts:
	phpBB/phpbb/session.php
[ticket/13234] Fix merge conflict

PHPBB3-13234
Merge pull request #3090 from Nicofuma/ticket/13234

Ticket/13234
Merge pull request #3091 from Nicofuma/ticket/13234-2

Ticket/13234 2
Merge branch 'develop-olympus' into prep-release-3.1.0
Merge branch 'prep-release-3.1.0' into develop-ascraeus