Fix TcpDuplexConnection using stats_ while it is null (#566)
Fix TcpDuplexConnection using stats_ while it is null (#566)

I've hit this with TcpConnectionFactory::createDuplexConnectionFromSocket() and
RSocketClient::fromConnection() already, just fix it in TcpDuplexConnection.
phoad/rsocket-cpp,alexmalyshev/rsocket-cpp,ReactiveSocket/reactivesocket-cpp,phoad/rsocket-cpp,alexmalyshev/rsocket-cpp,phoad/rsocket-cpp,phoad/rsocket-cpp,alexmalyshev/rsocket-cpp,phoad/rsocket-cpp,rsocket/rsocket-cpp,ReactiveSocket/reactivesocket-cpp,rsocket/rsocket-cpp,rsocket/rsocket-cpp,ReactiveSocket/reactivesocket-cpp,alexmalyshev/rsocket-cpp,rsocket/rsocket-cpp