Set pty serial port to NULL by default

pttyhandler.cpp

@@ -240,7 +240,7 @@ void pttyHandler::receiveDataIn(int fd) {
 void pttyHandler::closePort()
 {
 #ifdef Q_OS_WIN
-    if (port)
+    if (port != Q_NULLPTR)
     {
         port->close();
         delete port;

pttyhandler.h

@@ -53,7 +53,7 @@ private:
     unsigned char buffer[256];
 
     QString portName;
-    QSerialPort* port;
+    QSerialPort* port = Q_NULLPTR;
     qint32 baudRate;
     unsigned char stopBits;
     bool rolledBack;