[ticket/12353] Fix displayed attachments in ACP

PHPBB3-12353
Merge remote-tracking branch 'Elsensee/ticket/12353' into develop-olympus

* Elsensee/ticket/12353:
  [ticket/12353] Fix displayed attachments in ACP
Merge branch 'develop-olympus' into develop-ascraeus

* develop-olympus:
  [ticket/12353] Fix displayed attachments in ACP