[HarfBuzz] Core Text backend not supporting font index

[Vincent Isambart]

Hi there,  

I had compiled HarfBuzz with Core Text support thinking it wouldn’t hurt, but I ended up losing a few hours today because the Core Text backend always loads the first font of a TTC file, ignoring the font index.

- Is this a known bug?
- Does anyone know a way it could be fixed? I looked at the Core Text and related APIs but couldn’t find anywhere you could specify which font you want to load inside of a TTC.
- If this cannot be fixed, would it be possible to have some sort of warning if you try to load a font with a font index > 0 with the Core Text backend, to prevent other people to lose time on this.

Thanks,
Vincent