Update to NZBGet formula to use a maintained version of libpar2

- As per the release notes for 0.13.0, NZBGet upstream suggests using
 libpar2 as it is maintained by Debian/Ubuntu team and has the patches
 (and other fixes) already applied
- Details here: http://nzbget.net/forum/viewtopic.php?f=4&t=1306
- Fixes #31015