OutgoingClient: Fix ssl connection/setting invalid ssl config

Constructing a `QSslConfiguration()` result in a null/empty
configuration. The fact that it worked with Qt 5 is pure luck, ie Qt bug.
The bug eventually get fixed in Qt 6 but not backported which lead to
this needed fix. We need to init from the default configuration else we
have no certificates filled.

src/client/QXmppOutgoingClient.cpp

@@ -129,13 +129,16 @@ void QXmppOutgoingClientPrivate::connectToHost(const QString &host, quint16 port
 {
     q->info(QString("Connecting to %1:%2").arg(host, QString::number(port)));
 
+    auto sslConfig = QSslConfiguration::defaultConfiguration();
+
     // override CA certificates if requested
     if (!config.caCertificates().isEmpty()) {
-        QSslConfiguration newSslConfig;
-        newSslConfig.setCaCertificates(config.caCertificates());
-        q->socket()->setSslConfiguration(newSslConfig);
+        sslConfig.setCaCertificates(config.caCertificates());
     }
 
+    // set new ssl config
+    q->socket()->setSslConfiguration(sslConfig);
+
     // respect proxy
     q->socket()->setProxy(config.networkProxy());