No CSV results in broken page

I found this line in /lib/

function csv_source( $atts ) {
        if ( isset( $atts['src'] ) || isset( $atts['source'] ) ) {
            $src = isset( $atts['source'] ) ? esc_url( $atts['source'] ) : esc_url( $atts['src'] );
            if ( 0 === strpos( $src, '/' ) )
                return home_url( $src );
            else
                return $src;
        }
        return CSV_06082013_URL . 'test.csv'; // Default file URL if no .csv file source is defined.

Which works perfectly if the URL is undefined.

Anybody know how to alter it so I can return the same ‘test.csv’ if the .csv file source is wrong?