JsonRpcConnection: don't write any data on shutdown

In fact, this is already done for the outer loop (for each bulk), just not yet for the inner one (for each message of a bulk). So once the remote signals EOF, don't try to get things done until write error (which can't be associated with a particular message anyway, due to buffering), but just let the peer go.

lib/remote/jsonrpcconnection.cpp

@@ -115,6 +115,10 @@ void JsonRpcConnection::WriteOutgoingMessages(boost::asio::yield_context yc)
 					if (m_Endpoint) {
 						m_Endpoint->AddMessageSent(bytesSent);
 					}
+
+					if (m_ShuttingDown) {
+						return;
+					}
 				}
 
 				m_Stream->async_flush(yc);