[ticket/12421] Don't parse [attachment] tags if user can't view them

https://tracker.phpbb.com/browse/PHPBB3-12421

PHPBB3-12421
[ticket/12421] Rebase and enable tests

PHPBB3-12421
Merge pull request #2330 from Nicofuma/ticket/12421

[ticket/12421] Don't parse [attachment] tags if user can't view them

* Nicofuma/ticket/12421:
  [ticket/12421] Rebase and enable tests
  [ticket/12421] Don't parse [attachment] tags if user can't view them