QFileDialog: don't warn about directory url prematurly

The app can set a directory url before showing the dialog.
Since we don't really know if the dialog is going to
be native or not at that point, it is too early to warn.

Change-Id: Ie9875ca90a500258841bad702ee864a46775641c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>

src/widgets/dialogs/qfiledialog.cpp

@@ -991,7 +991,7 @@ void QFileDialog::setDirectoryUrl(const QUrl &directory)
         d->setDirectory_sys(directory);
     else if (directory.isLocalFile())
         setDirectory(directory.toLocalFile());
-    else
+    else if (d->usingWidgets())
         qWarning() << "Non-native QFileDialog supports only local files";
 }