bug#26742: Display bug with composed strings

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: clement.pitclaudel@live.com,  26742@debbugs.gnu.org
> Date: Tue, 02 May 2017 21:06:44 +0200
> 
> On Mai 02 2017, Eli Zaretskii <eliz@gnu.org> wrote:
> 
> > Also, what happens if you replace 8804 in your test file with 10877?
> 
> Interestingly, this is also shows the effect, even though both
> characters are taken from the same font (not the default font).

So this conclusion:

> So the conclusion this far is that the feature only works reliably
> when both characters are displayed by the same font.

appears to be incorrect, and there's some other factor at work here.