bug#56393: Actually fix the long lines display bug

[Gerd Möllmann]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> Which leaves me with something to think about, of course: when redisplay
> sets the flag in the buffer, then there's of course a time before that.
> And the question is what can happen in that interval.  But not today.
> I'll come back to you.

So far, I can't think of something specifically catastrophic happening
in the interval between a buffer being loaded, let's say, and it being
marked with the flag.

I think it's the same situation we talked about previously wrt a buffer
that is never or not yet displayed:

Pretty much anything could potentially happen as soon as an iterator is
used.  The reason for this is that iterators must know faces and other
stuff, let's simply say they must know text properties and overlays.
And that can call Lisp, and then all bets are off.

If that happens in practice, how often it happens, or what else, I don't
know.

What's the worst thing that can happen?  Slowness, I guess.  I can't
think of something going seriously down the drain ATM.


I guess that's about what I can continute to the whole matter.

Nice work.  THanks!