WelcomeScreen: Don't rely on image format auto-detection

The examples and marketplace pages show images that are decoded from
data buffers. This happened without specifying the encoding format,
which triggers image auto-detection.

The negligible overhead of the auto-detection is usually not a problem,
but the probing of image QImageIOHandlers that goes along with auto-
detection can emit warnings. A concrete example is a warning in the TGA
plugin which was added in Qt 5.15.1.

Task-number: QTCREATORBUG-24853
Change-Id: I596604bde7621acf92e825f45e0c23ac4e90b78d
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/marketplace/productlistmodel.cpp

@@ -33,6 +33,7 @@
 #include <utils/qtcassert.h>
 
 #include <QDesktopServices>
+#include <QFileInfo>
 #include <QJsonArray>
 #include <QJsonDocument>
 #include <QJsonObject>
@@ -380,7 +381,8 @@ void SectionedProducts::onImageDownloadFinished(QNetworkReply *reply)
     if (reply->error() == QNetworkReply::NoError) {
         const QByteArray data = reply->readAll();
         QPixmap pixmap;
-        if (pixmap.loadFromData(data)) {
+        const QString imageFormat = QFileInfo(reply->request().url().fileName()).suffix();
+        if (pixmap.loadFromData(data, imageFormat.toLatin1())) {
             const QString url = reply->request().url().toString();
             QPixmapCache::insert(url, pixmap.scaled(ProductListModel::defaultImageSize,
                                                     Qt::KeepAspectRatio, Qt::SmoothTransformation));