[OT] Add SubstLookup serialize API

src/hb-ot-layout-common-private.hh

diff --git a/src/hb-ot-layout-common-private.hh b/src/hb-ot-layout-common-private.hh
index dcd4ed1..5c51ee5 100644
--- a/src/hb-ot-layout-common-private.hh
+++ b/src/hb-ot-layout-common-private.hh
@@ -323,7 +323,7 @@
     lookupType.set (lookup_type);
     lookupFlag.set (lookup_props & 0xFFFF);
     if (unlikely (!subTable.serialize (c, num_subtables))) return TRACE_RETURN (false);
-    if ((lookup_props >> 16) || lookupFlag & LookupFlag::UseMarkFilteringSet)
+    if (lookupFlag & LookupFlag::UseMarkFilteringSet)
     {
       USHORT &markFilteringSet = StructAfter<USHORT> (subTable);
       markFilteringSet.set (lookup_props >> 16);