[kern/kerx] Fix trace numbering

src/hb-aat-layout-kerx-table.hh

@@ -720,6 +720,7 @@ struct kerx
 
     skip:
       table = &StructAfter<KerxTable> (*table);
+      c->set_lookup_index (c->lookup_index + 1);
     }
   }
 

src/hb-ot-kern-table.hh

@@ -596,6 +596,7 @@ struct KernTable
 
     skip:
       st = &StructAfter<SubTable> (*st);
+      c->set_lookup_index (c->lookup_index + 1);
     }
   }