message: Fix potential segfault in private_thread
diff: @@ -91,8 +91,8 @@ void private_thread::exec(private_thread* this_ptr) {
  // detached actor is destroyed and this object is unreachable
  this_ptr->await_self_destroyed();
  // signalize destruction of detached thread to registry
  - this_ptr->system_.dec_detached_threads();
  this_ptr->system_.thread_terminates();
  + this_ptr->system_.dec_detached_threads();
  // done
  delete this_ptr;
  }
  