Tiny improvement on previous commit

Functionally the same.

src/hb-blob.hh

@@ -90,6 +90,7 @@ struct hb_blob_ptr_t
   unsigned int get_length () const { return b.get ()->length; }
   void destroy () { hb_blob_destroy (b.get ()); b = nullptr; }
 
+  private:
   hb_nonnull_ptr_t<hb_blob_t> b;
 };
 

src/hb-null.hh

@@ -177,6 +177,7 @@ struct hb_nonnull_ptr_t
   T * get () const { return v ? v : const_cast<T *> (&Null (T)); }
   T * get_raw () const { return v; }
 
+  private:
   T *v;
 };
 

src/hb-ot-layout-gsubgpos.hh

@@ -3380,7 +3380,7 @@ struct GSUBGPOS
       if (unlikely (!this->accels))
       {
 	this->lookup_count = 0;
-	hb_blob_destroy (this->table.get_blob ());
+	this->table.destroy ();
 	this->table = hb_blob_get_empty ();
       }