[ticket/12518] Apply De Morgan to make the conditions easier to read

PHPBB3-12518
Merge pull request #2446 from nickvergessen/ticket/12518

[ticket/12518] Apply De Morgan to make the conditions easier reasable

* nickvergessen/ticket/12518:
  [ticket/12518] Apply De Morgan to make the conditions easier to read
[ticket/12534] Do not abuse errorbox for en/disable confirmation of extensions

PHPBB3-12534
[ticket/12534] Do not use errorbox for multi steps

PHPBB3-12534
[ticket/12534] Fix filter for functional tests

PHPBB3-12534
Merge remote-tracking branch 'nickvergessen/ticket/12534' into develop-ascraeus

* nickvergessen/ticket/12534:
  [ticket/12534] Fix filter for functional tests
  [ticket/12534] Do not use errorbox for multi steps
  [ticket/12534] Do not abuse errorbox for en/disable confirmation of extensions