bug#57669: 29.0.50; C-n, C-p off under long lines

[Eli Zaretskii]

> From: dick <dick.r.chiang@gmail.com>
> Cc: 57669@debbugs.gnu.org
> Date: Fri, 09 Sep 2022 15:28:47 -0400
> 
> You want proof?  Okay:
> 
> src/emacs -Q src/xdisp.c

Sure, showing off display of a pure-ASCII file that uses a single font
proves your case!  (It actually proves mine.)

> I trust you'll find no gui features missing between it and GNU Emacs.  I
> would further show that my changes do not include ones which, and I
> quote, "are plain wrong," but it's much harder to prove the
> non-existence of bugs (wouldn't that be nice) than it is for you to
> prove their existence.

Once again, and for the last time: show your code which deals with
long lines; explain what it does and how.  Then this discussion may
have some value.