[ticket/13174] Add missing closing </div> to ucp_pm_viewmessage

PHPBB3-13174
Merge remote-tracking branch 'PayBas/ticket/13174' into develop-ascraeus

* PayBas/ticket/13174:
  [ticket/13174] Add missing closing </div> to ucp_pm_viewmessage
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/13174] Add missing closing </div> to ucp_pm_viewmessage