Prevent hang in case of connecting to old server not supporting new h…

…andshake value

src/wesnothd_connection.cpp

@@ -165,6 +165,9 @@ void wesnothd_connection::handle_handshake(const error_code& ec)
 {
 	MPTEST_LOG;
 	if(ec) {
+		if(ec == boost::asio::error::eof) {
+			throw std::runtime_error("Failed to complete handshake with server");
+		}
 		LOG_NW << __func__ << " Throwing: " << ec << "\n";
 		throw system_error(ec);
 	}