SearchNumericRange min/max is zero when it should be null

Suggested release note:

A faceted Full-Text Search result's `SearchNumericRange.min()` and `max()` methods now correctly return null instead of zero when the respective range endpoint is unbounded.

When specifying an FTS facet with a numeric range, if the range's min or max is unbounded, the `SearchNumericRange` in the result should have null for the unbounded endpoint. Instead, the unbounded endpoint is set to zero.