[InterNetNews/inn] fcb099: Add a special comment in response to MAXARTNUM

[Julien ÉLIE]

  Branch: refs/heads/main
  Home:   https://github.com/InterNetNews/inn
  Commit: fcb09930eaafbdaefeb2aee989fc8658f973af23
      https://github.com/InterNetNews/inn/commit/fcb09930eaafbdaefeb2aee989fc8658f973af23
  Author: Julien ÉLIE <Julien-Elie at users.noreply.github.com>
  Date:   2023-01-23 (Mon, 23 Jan 2023)

  Changed paths:
    M innd/nc.c
    M nnrpd/nnrpd.c

  Log Message:
  -----------
  Add a special comment in response to MAXARTNUM

As INN does not handle article numbers greater than 2^31-1, there's no
point in implementing the MAXARTNUM command.  Just return 500 but with
a special comment mentioning our 2^31-1 limit.