Fix inifinite loop in findCommonPrefixForUrls

Some mimetypes apply to files without extensions and only the filename.

autotests/kerfuffle/addtoarchivetest.cpp

@@ -98,6 +98,13 @@ void AddToArchiveTest::testCompressHere_data()
         << QStringLiteral("test-3.4.0.tar.gz")
         << 2ULL;
 
+    QTest::newRow("compress here (as TAR) - files with mimetypes but no extension (no infinite loop)")
+        << QStringLiteral("tar.gz")
+        << Archive::Unencrypted
+        << QStringList {QFINDTESTDATA("data/Makefile"), QFINDTESTDATA("data/README")}
+        << QStringLiteral("Archive.tar.gz")
+        << 2ULL;
+
     if (!PluginManager().preferredWritePluginsFor(QMimeDatabase().mimeTypeForName(QStringLiteral("application/zip"))).isEmpty()) {
         QTest::newRow("compress here (as ZIP) - dir with files")
             << QStringLiteral("zip")

kerfuffle/addtoarchive.cpp

@@ -211,7 +211,11 @@ QString findCommonPrefixForUrls(const QList<QUrl> &list)
         // Strip filename of its extension, but only if present (see #362690).
         // Use loops to handle cases like `*.tar.gz`.
         while (!QMimeDatabase().mimeTypeForFile(fileName, QMimeDatabase::MatchExtension).isDefault()) {
-            fileName = QFileInfo(fileName).completeBaseName();
+            const QString strippedName = QFileInfo(fileName).completeBaseName();
+            if (strippedName == fileName) {
+                break;
+            }
+            fileName = strippedName;
         }
 
         if (prefix.length() > fileName.length()) {