FileDownloader: Do not assume existence of QQmlData

QQmlData::wasDeleted returns a sensible result, even when the QQmlData
has not been created (for instance because the object was not
instantiated by the QML engine). Checking the result of
QQmlData::get is counterproductive, as FileDownloader objects are for
instance created by ContentLibraryMaterialsModel::fetchBundleIcons,
without going through the QML engine.

Moreover, try to log some information about why we ended up with a
network error.

Task-number: QDS-9687
Change-Id: Icf7fba94a8a0552305ac39f2caa32426e58972a0
Reviewed-by: Henning Gründl <henning.gruendl@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/qmldesigner/utils/filedownloader.cpp

@@ -258,18 +258,16 @@ void FileDownloader::doProbeUrl()
     QNetworkReply::connect(reply,
                            &QNetworkReply::errorOccurred,
                            this,
-                           [this](QNetworkReply::NetworkError) {
+                           [this](QNetworkReply::NetworkError code) {
-                               QQmlData *data = QQmlData::get(this, false);
-                               if (!data) {
-                                   qDebug() << Q_FUNC_INFO << "FileDownloader is nullptr.";
-                                   return;
-                               }
 
                                if (QQmlData::wasDeleted(this)) {
                                    qDebug() << Q_FUNC_INFO << "FileDownloader was deleted.";
                                    return;
                                }
 
+                               qDebug() << Q_FUNC_INFO << "Network error:" << code
+                                        << qobject_cast<QNetworkReply *>(sender())->errorString();
+
                                m_available = false;
                                emit availableChanged();
                            });