bug#56683: 29.0.50; long lines fix doesn't work correctly when lines are truncated

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: andreyorst@gmail.com,  56683@debbugs.gnu.org,  gregory@heytings.org
> Date: Fri, 22 Jul 2022 15:54:07 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > That feature is disabled by default.  If enabled, then yes, it will
> > most probably fire before that.
> 
> Could we enabled it automatically when we switch on iterator narrowing?

Technically, sure.  I'm not yet convinced we should, though, because
it isn't clear to me what problems, if any, will be left after the
narrowing idea is used as fully as practical.