[HarfBuzz] please remove U+115F U+1160 from default_ignorable

[Dohyun Kim]

2013/3/19 Konstantin Ritt <ritt.ks at gmail.com>:
>
> IIUC, a correct solution would be determining Hangul clusters and then
> setting the "accumulated" cluster advance to the cluster base prior to
> hiding default ignorables. Correct me if I'm wrong.
>

Well, this solution will give us corrent output only in its appearance.

If "hiding default ignorable" means substituting by zero-width space,
then the pdf file produced by xetex would not contain U+115F and
U+1160, resulting in invalid text string when texts are extracted from
the pdf.

Only isolated filler may be ignored. Anyway this is illegal input string.

Best,
Dohyun Kim