Suppress exception when mapping field of unknown type

By default, the FilterDataSet class will iterate over all fields and use CastAndCall on each one to call the subclass' mapping function with the appropriate array type.

This only works if the array is of a known type. If it is not CastAndCall throws an exception. However, having the entire filter exception out just because one field cannot be converted does not make sense. Instead, catch the exception, log a warning, and drop the field.