[subset] Map glyphs during SingleSubst subsetting

Ha!

src/hb-ot-layout-gsub-table.hh

@@ -110,6 +110,7 @@ struct SingleSubstFormat1
   inline bool subset (hb_subset_context_t *c) const
   {
     TRACE_SUBSET (this);
+    const hb_map_t &glyph_map = *c->plan->glyph_map;
     hb_vector_t<GlyphID> from;
     hb_vector_t<GlyphID> to;
     hb_codepoint_t delta = deltaGlyphID;
@@ -117,8 +118,8 @@ struct SingleSubstFormat1
     {
       if (!c->plan->glyphset->has (iter.get_glyph ()))
         continue;
-      from.push ()->set (iter.get_glyph ());
-      to.push ()->set ((iter.get_glyph () + delta) & 0xFFFF);
+      from.push ()->set (glyph_map[iter.get_glyph ()]);
+      to.push ()->set (glyph_map[(iter.get_glyph () + delta) & 0xFFFF]);
     }
     c->serializer->err (from.in_error () || to.in_error ());
 
@@ -216,14 +217,15 @@ struct SingleSubstFormat2
   inline bool subset (hb_subset_context_t *c) const
   {
     TRACE_SUBSET (this);
+    const hb_map_t &glyph_map = *c->plan->glyph_map;
     hb_vector_t<GlyphID> from;
     hb_vector_t<GlyphID> to;
     for (Coverage::Iter iter (this+coverage); iter.more (); iter.next ())
     {
       if (!c->plan->glyphset->has (iter.get_glyph ()))
         continue;
-      from.push ()->set (iter.get_glyph ());
-      to.push ()->set (substitute[iter.get_coverage ()]);
+      from.push ()->set (glyph_map[iter.get_glyph ()]);
+      to.push ()->set (glyph_map[substitute[iter.get_coverage ()]]);
     }
     c->serializer->err (from.in_error () || to.in_error ());