multiple cuts returns empty results if one of them is not found in cube

[davelandry]

Moving from Datawheel/canon#316

@MarcioPorto this is the one you're working on, right?

The expected behavior would be to return data for any valid cuts (and ignore the invalid cut IDs).

[jazzido]

Just for the record: let's implement this one with an optional boolean parameter (&validate_cuts={true, false}). It should default to true.