SerialPort PinoutSignalsEventNotifier blindly reads pinout signals when serial port is in error

When a port error occurs, f.ex. an USB adapter is unplugged, readPinoutSignals() will blindly continue to call mSerialPort->pinoutSignals();

This will produce QSerialPort to emit errorOccured() each time.

We should check the QSerialPort::error() before read. Also, when a read fails, we should tell that the pinout signals is not reliable. This means, we no longer directly emit PinoutSignals, but some container class that also indicates if we have signals or an error.

Notice that this would also require PinoutSignalUiState to handle some error / uncertainty state.