[HarfBuzz] Space glyph generated for zwj

[Muller, Eric]

For the text <U+0915, U+094D, U+200D, U+0020>, I get:

emuller> hb-shape ~/fonts/noto/NotoSansDevanagari-Regular.ttf 'क्‍ '
[gid183=0+1204|gid3=2+0|gid3=3+532]

which means that a zero-width space glyph is generated for the U+200D. I 
expected just:

[gid183=0+1204|gid3=3+532]

Is there a good reason for that choice?

Thanks,
Eric.