Background: In setWindowFields, you can use window: {range: [lower, upper]} to define a window in terms of the values in the collection.  We only support numbers and dates.  If setWindowFields finds a value with the wrong type, it uasserts.

However, our fuzzer found a case where it tasserts instead of uasserts.  If the range is [+N, unbounded], and the input has an unexpected type, we can tassert when computing the right endpoint for the 'unbounded' part.