bug#56393: Actually fix the long lines display bug

[Eli Zaretskii]

> Date: Wed, 06 Jul 2022 17:17:25 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: gerd.moellmann@gmail.com, larsi@gnus.org, 56393@debbugs.gnu.org
> 
> > Then maybe try to increase your keyboard auto-repeat rate?
> 
> The default auto-repeat rate on my system is 25.  I tried with 30, 35 and 
> 40, Emacs is still as responsive.  With 45 your recipe works, I see some 
> chokes.  Why is that a problem?

Because I think we should understand the reason.  I suspect the buffer
doesn't get narrowed or something.