[ticket/12667] Do not point viewtopic URL to unread post outside of view=unread

PHPBB3-12667
Merge pull request #2568 from prototech/ticket/12667

[ticket/12667] Do not point viewtopic URL to unread post outside of view=unread.

* prototech/ticket/12667:
  [ticket/12667] Do not point viewtopic URL to unread post outside of view=unread