Get the randomizer from shared device, which is an object of dcpp::shared_device.
Calling Sig:
dcpp::IRandomizer * randomizer = shared_device.randomizer();
// Can use auto.
shared_device.randomizer() do check-throw exception.
Set a new randomizer to the engine, if the new set randomizer is invalid, do nothing.
Calling Sig:
shared_device.randomizer(new_randomizer);