[object] Only destruct object if it's not trivially-destructible

Such that we're legally free to access the object to destruct its
(pointer) fields ourselves afterwards.  For things like hb_font_t,
hb_face_t, etc.

src/hb-object.hh

@@ -273,6 +273,7 @@ static inline bool hb_object_destroy (Type *obj)
 
   hb_object_fini (obj);
 
+  if (!std::is_trivially_destructible<Type>::value)
     obj->~Type ();
 
   return true;