[HarfBuzz] Valid range of deltaGlyphID is too small

[Dohyun Kim]

Hi,

While testing harfbuzz-ng with a huge font which has more than 64,000
glyphs, I encountered a strange result of hb-shape:

  <uniAC00=0+970|gid-1389=0|uniB098=6+970|gid-1388=6>

As shown, minus GID numbers are printed on the screen; this of course
is not valid.

The problem seems to occur because of the valid range of deltaGlyphID
in hb-ot-layout-gsub-table.hh.
After having changed 67th line of hb-ot-layout-gsub-table.hh from

  SHORT         deltaGlyphID;           /* Add to original GlyphID to get

to

  USHORT        deltaGlyphID;           /* Add to original GlyphID to get

the problem disappeared and correct glyph names were printed instead
of minus GIDs.

I have no idea about whether USHORT typecast is good for this case.
Anyway, changing to USHORT has solved an issue which has nagged me for months.

Best,
-- 
Dohyun Kim
College of Law, Dongguk University
Seoul, Republic of Korea