Get the event receiver from shared device, which is an object of dcpp::shared_device.
Calling Sig:
dcpp::IEventReceiver * receiver = shared_device.receiver();
// Can use auto.
If it has no event receiver, it returns nullptr, instead of throwing exception.
Set a new event receiver to the engine, if the new set event receiver is nullptr, the previous event receiver will be cleared.
Calling Sig:
shared_device.receiver(new_receiver);