CumulativeAnalyzableBase.ComputeByIndexImpl call ComputeCumulativeValue twice for the same index

[ljason1]

The line #43 of CumulativeAnalyzableBase.cs should be LastCacheIndex = index; instead of LastCacheIndex = index - 1;
it make ComputeCumulativeValue be called twice for the same index (cause ParabolicStopAndReverse calculate wrong values)