javascript error when select a area on the chart.

[hudannis]

When select an area and then click the chart to clear the selection, javascript error occurs. ame thing can be reproduced on the example page(http://nickqizhu.github.io/dc.js/), by selecting on the "Monthly Index Abs Move..." chart.

function rangesEqual(range1, range2) {
    if (!range1 && !range2) {
        return true;
    }

    if (range1.length === 0 && range2.length === 0) {★range1 is null
        return true;
    }

    if (range1 && range2 &&
        range1[0].valueOf() === range2[0].valueOf() &&
        range1[1].valueOf() === range2[1].valueOf()) {
        return true;
    }

    return false;
}

[gordonwoodhull]

Fixed by #489