bug#56682: locked narrowing

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: dgutov@yandex.ru,  56682@debbugs.gnu.org,  gregory@heytings.org
> Date: Wed, 17 Aug 2022 16:09:09 -0400
> 
> >> Why do we flush the cache when `just_this_one_p` is false?
> > Because it means many things could have changed,
> 
> I can't see which ones that could be.

just_this_one_p is true when we are only redisplaying the selected
window.