[HarfBuzz] Setting initial cluster value

[Khaled Hosny]

On Sat, Jun 25, 2016 at 01:07:29PM -0400, Kelvin Ma wrote:
> for the same reason kerning cannot happen between two different font runs,
> how can arabic shaping happen across different font runs?

Basic Arabic shaping involves textual analysis, this depends on Unicode
character properties and neighboring characters and is font independent,
so it can be done across different fonts.

Regards,
Khaled