Add Qt version check for errorOccurred()

Author: softins

src/client.cpp

@@ -266,13 +266,17 @@ void CClient::OnSendCLProtMessage ( CHostAddress InetAddr, CVector<uint8_t> vecM
         // create a TCP client connection and send message
         QTcpSocket* pSocket = new QTcpSocket ( this );
 
+#if QT_VERSION >= QT_VERSION_CHECK( 5, 15, 0 ) // earlier versions don't work
         connect ( pSocket, &QTcpSocket::errorOccurred, this, [this, pSocket] ( QAbstractSocket::SocketError err ) {
             Q_UNUSED ( err );
 
             qWarning() << "- TCP connection error:" << pSocket->errorString();
             // may want to specifically handle ConnectionRefusedError?
             pSocket->deleteLater();
         } );
+#else
+#    warning "QTcpSocket::errorOccurred requires Qt >= 5.15.0"
+#endif
 
         connect ( pSocket, &QTcpSocket::connected, this, [this, pSocket, InetAddr, vecMessage]() {
             // connection succeeded, give it to a CTcpConnection