serial: clear handle fd on error to prevent spurious close() in serial_close()

src/serial.c

@@ -232,6 +232,7 @@ int serial_open_advanced(serial_t *serial, const char *path, uint32_t baudrate,
     if (tcsetattr(serial->fd, TCSANOW, &termios_settings) < 0) {
         int errsv = errno;
         close(serial->fd);
+        serial->fd = -1;
         return _serial_error(serial, SERIAL_ERROR_CONFIGURE, errsv, "Setting serial port attributes");
     }