Calculate the min and max values for this series's yField(s). Takes into account yField
combinations, exclusions, and stacking.
@return {Array} [min, max]
function() {
        var me = this,
            chart = me.chart,
            store = chart.getChartStore(),
            data = store.data.items,
            count = me.getRecordCount(),
            i, ln, record,
            stacked = me.stacked,
            min, max,
            positiveTotal, negativeTotal;

        function eachYValueStacked(yValue, i) {
            if (!me.isExcluded(i)) {
                if (yValue < 0) {
                    negativeTotal += yValue;
                } else {
                    positiveTotal += yValue;
                }
            }
        }

        function eachYValue(yValue, i) {
            if (!me.isExcluded(i)) {
                if (yValue > max) {
                    max = yValue;
                }
                if (yValue < min) {
                    min = yValue;
                }
            }
        }

        if (count > 0) {
            min = Infinity;
            max = -min;
            
            for (i = 0, ln = data.length; i < ln; i++) {
                record = data[i];
                if (stacked) {
                    positiveTotal = 0;
                    negativeTotal = 0;
                    me.eachYValue(record, eachYValueStacked);
                    if (positiveTotal > max) {
                        max = positiveTotal;
                    }
                    if (negativeTotal < min) {
                        min = negativeTotal;
                    }
                } else {
                    me.eachYValue(record, eachYValue);
                }
            }
            
            // If we made no progress, treat it like a category axis
            if (min == Infinity) {
                min = 0;
            }
            
            if (max == -Infinity) {
                max = count - 1;
            }
        } else {
            min = max = 0;
        }
        return [min, max];
    }