QmlDesigner: Skip duplicate assets imported simultaneously

Since asset folder is generated from the asset filename without
suffix, it is possible to select multiple assets with same filename
but different suffix into the import, and they would import into the
same asset directory, causing confusion and potentially broken import.

Fixed by skipping duplicate assets within the same import.

Change-Id: Ied825f32309b4321de7fa471cbd5ff1041e03072
Fixes: QDS-1239
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>

src/plugins/qmldesigner/components/itemlibrary/itemlibraryassetimporter.cpp

@@ -275,6 +275,11 @@ void ItemLibraryAssetImporter::parseQuick3DAsset(const QString &file, const QVar
 
     QString targetDirPath = targetDir.filePath(assetName);
 
+    if (outDir.exists(assetName)) {
+        addWarning(tr("Skipped import of duplicate asset: \"%1\"").arg(assetName));
+        return;
+    }
+
     if (targetDir.exists(assetName)) {
         if (!confirmAssetOverwrite(assetName)) {
             addWarning(tr("Skipped import of existing asset: \"%1\"").arg(assetName));