Don't use deprecated QAbstractSocket::error()

src/base/net/smtp.cpp

@@ -113,8 +113,12 @@ Smtp::Smtp(QObject *parent)
 
     connect(m_socket, &QIODevice::readyRead, this, &Smtp::readyRead);
     connect(m_socket, &QAbstractSocket::disconnected, this, &QObject::deleteLater);
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 15, 0))
+    connect(m_socket, &QAbstractSocket::errorOccurred, this, &Smtp::error);
+#else
     connect(m_socket, qOverload<QAbstractSocket::SocketError>(&QAbstractSocket::error)
             , this, &Smtp::error);
+#endif
 
     // Test hmacMD5 function (http://www.faqs.org/rfcs/rfc2202.html)
     Q_ASSERT(hmacMD5("Jefe", "what do ya want for nothing?").toHex()