bug#41645: 27.0.91; Combining Grapheme Joiner (#x34f) gui artifacts

[Eli Zaretskii]

> From: Pip Cet <pipcet@gmail.com>
> Cc: dfussner@googlemail.com,  41645@debbugs.gnu.org
> Date: Thu, 04 Jun 2020 22:48:19 +0000
> 
> > The IT_CHARACTER case also does this when the pixel width comes out as
> > zero:
> >
> >           it->phys_ascent = it->ascent;
> >           it->phys_descent = it->descent;
> 
> > That is, it doesn't trust the ascent/descent values from metrics.
> > Should we do the same for compositions, or did you see any reasons to
> > believe the metrics in this case?
> 
> The former, I believe. I still think fonts with such glyphs are broken,
> and we should rely as little as possible on what they say about them.
> 
> So I've done that in this new version.

Thanks.  Please push to the master branch, with one nit:

> +  if (glyph_not_available_p)
> +    {
> +      s->font_not_found_p = true;
> +    }

Our style convention is not to use braces when the block entails only
one line.