bug#56393: Actually fix the long lines display bug

[Eli Zaretskii]

> Cc: 56393@debbugs.gnu.org
> Date: Tue, 19 Jul 2022 08:58:52 +0000
> From: Gregory Heytings <gregory@heytings.org>
> 
> 
> >> - I did not see that l_l_o_p is set to false anywhere.  Should it be? 
> >> What if a buffer is modified in such a way that there are no long lines 
> >> anymore?
> >
> > Gosh!  That was an error, thanks!
> >
> 
> In fact it wasn't, there is a "b->long_line_optimizations_p = 0;" in 
> reset_buffer.

But who calls reset_buffer when a buffer is being edited?