Add ASSERT_POD for most objects
diff --git a/src/hb-blob.cc b/src/hb-blob.cc
index f90f97e..3cc2d9d 100644
--- a/src/hb-blob.cc
+++ b/src/hb-blob.cc
@@ -48,6 +48,7 @@
 
 struct _hb_blob_t {
   hb_object_header_t header;
+  ASSERT_POD ();
 
   bool immutable;