[ticket/11292] Fix: Newlines removed in display of PM reports

Report text is run through make_clickable and bbcode_nl2br for PMs
just as it is for posts.

PHPBB3-11292
Merge remote-tracking branch 'gn36/ticket/11292' into develop-olympus

* gn36/ticket/11292:
  [ticket/11292] Fix: Newlines removed in display of PM reports