Fix QDDSHandler::canRead to return false in case of a scan error.

Change-Id: If776b122c90d79d430916677a46684770870956a
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Alex Char <prevedtest@gmail.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>