Fix Histogram filter range for DataSet
In the transition of the `Histogram` filter to the new filter types, a bug was introduced. The `Histogram` filter has an option to set the range for which to compute the histogram. (The range of the data will be used instead if none is specified.) This range was properly used when computing the histogram on a `PartitionedDataSet`. However, when running on a single `DataSet`, the new filter structure skipped over the partition code that checked to see if the range was specified. (It also skipped over the code that properly computed the range in MPI.) This change properly checks to see if `Execute` was called with a single `DataSet` and updates the `ComputedRange` appropriately.