[HarfBuzz] Fixing Khmer U+17DD

[Martin Hosken]

Dear Behdad,

Khmer has a rare character U+17DD used by linguists and minorities and it isn't shaping correctly in that there is a dotted circle inserted if it occurs before U+17C8. The fix to this is to change the test for vowel to include U+17DD.

In hb-ot-shape-complex-indic.cc, near the start of set_indic_properties there is a test of hb_in_range(u, 0x17CB, 0x17D3) this would need an extra || u == 0x17DD.

TIA,
Yours,
Martin