Fix series length on binary series op series operations

[kylebrandt]

in biSeriesSeries the length of the resulting series is the result of A when A + B. However, only points where there time matches for both A and B are added to the result. This results in a series with a bunch of null points and the Grafana displaying (datapoints outside timerange) in the graph.

func biSeriesSeries(name string, labels dataframe.Labels, op string, aSeries, bSeries Series) (Series, error) {
	newSeries := NewSeries(name, labels, aSeries.Len())
	for aIdx := 0; aIdx < aSeries.Len(); aIdx++ {
		aTime, aF := aSeries.GetPoint(aIdx)
		for bIdx := 0; bIdx < bSeries.Len(); bIdx++ {
			bTime := bSeries.GetTime(bIdx)
			if *aTime == *bTime {
				bF := bSeries.GetValue(bIdx)
				if aF == nil || bF == nil {
					newSeries.SetPoint(aIdx, aTime, nil)
					break
				}
				nF, err := binaryOp(op, *aF, *bF)
				if err != nil {
					return newSeries, err
				}
				newSeries.SetPoint(aIdx, aTime, &nF)
				break
			}
		}
	}
	return newSeries, nil
}