Further adjust mark advance zeroing

This is a followup to 568000274c8edb5f41bc4f876ce21fcc8bdaeed8.
Looks like in the Latin shaper, Uniscribe zeroes all Unicode NSM
advances *after* GPOS, not before.  Match that.

Can be tested using DejaVu Sans Mono, since that font has GPOS
rules to zero the mark advances on its own.
1 file changed