Native crash in objects derived from ResultSet

Any object obtained from a ResultSet, a Result, a Dictionary, an Array, etc, cannot be used once the ResultSet that owns the c4QueryEnum has been closed.

Closing the ResultSet will free the query enumerator and subsequent references to the Fleece data underlying it will have unpredictable results.

Any reference to any object that can be obtained from a QueryResult should fail immediatly, if the QueryResult that owns it has been closed.