message: don't use std::isnan
diff: @@ -423,7 +423,7 @@ bool Motor::measure_phase_resistance(float test_current, float max_voltage) {
  disarm();
  config_.phase_resistance = control_law.get_resistance();
  - if (std::isnan(config_.phase_resistance)) {
  + if (is_nan(config_.phase_resistance)) {
  // TODO: the motor is already disarmed at this stage. This is an error
  // that only pretains to the measurement and its result so it should
  // just be a return value of this function.
  