Add default_shaper_list to shape_plan

src/hb-shape-plan-private.hh

diff --git a/src/hb-shape-plan-private.hh b/src/hb-shape-plan-private.hh
index 1b3c3b2..d6a57d6 100644
--- a/src/hb-shape-plan-private.hh
+++ b/src/hb-shape-plan-private.hh
@@ -39,6 +39,7 @@
   hb_object_header_t header;
   ASSERT_POD ();
 
+  hb_bool_t default_shaper_list;
   hb_face_t *face;
   hb_segment_properties_t props;