[repacker] Use extension promotion when repacking invoked via hb-subset-repacker (eg. from fonttools).
diff --git a/src/hb-subset-repacker.cc b/src/hb-subset-repacker.cc
index 03e3feb..99dc69b 100644
--- a/src/hb-subset-repacker.cc
+++ b/src/hb-subset-repacker.cc
@@ -44,6 +44,9 @@
   for (unsigned i = 0 ; i < num_hb_objs ; i++)
     packed.push (&(hb_objects[i]));
 
-  return hb_resolve_overflows (packed, HB_OT_TAG_GSUB);
+  return hb_resolve_overflows (packed,
+                               HB_OT_TAG_GSUB,
+                               20,
+                               true);
 }
 #endif