bug#42256: 27.0.50; composition

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: rms@gnu.org,  42256@debbugs.gnu.org
> Date: Wed, 15 Jul 2020 02:20:50 +0300
> 
> > I suggest to look at the code which displays the "Composed with" line
> > and decides which characters to show there, and do the same in your
> > addition.
> 
> Do you think it's now better?

It is much better, thanks.  But there is still one small glitch: try
"C-u C-x =" on buffer position 872 in HELLO, and you will see that
U+0651 ARABIC SHADDA is displayed as an empty box.  By contrast, the
"Composed with" line displays the shadda correctly.  I think this is
because you display only a single character (by using 'aref'), whereas
combining characters need to be surrounded by TABs to display
correctly without combining with their neighbors.