bug#20984: 25.0.50; Combining accents don't display properly in certain fonts

[Eli Zaretskii]

> From: handa <handa@gnu.org>
> Cc: bruce.connor.am@gmail.com, 20984@debbugs.gnu.org
> Date: Mon, 06 Jul 2015 23:59:14 +0900
> 
> > >   [0 1 0 626 8 1 6 8 -3 nil]
> > >   [0 1 0 734 0 1 5 11 -9 [0 0 0]]
> 
> I tried that font on my Lubuntu system with Emacs 24.5 and the latest
> trunk version.  I see no problem with 24.5, i.e. a-grave is correctly
> displayed, but see the same problem as yours with trunk version.
> 
> So, it seems that something was broken recently.

Could it be my latest changes related to fontsets?  Though then the
Windows build should have been affected as well.

The composition data above looks wrong, doesn't it?  Like if the 'a'
part of the grapheme cluster comes from some different codepoint, not
from 'a', am I right?