Returns the order of the field if successful and FAIL (or -1) otherwise.
Description
VFfieldorder returns the order of the vdata field identified by its index, field_index, in the vdata identified by the parameter vdata_id.
The value of the parameter field_index ranges from 0 to the total number of fields in the vdata - 1. The number of vdata fields is returned by VFnfields function.