readField method
Reads a single field from the current record and returns it. Remember to call {@link #read()} before starting to read fields from the dbf, and call it every time you need to move to the next record.
@param fieldNum The field number to be read (zero based) @ If an error occurs. @return The value of the field
Implementation
Future<dynamic> readField(final int fieldNum) async {
return await readObject(fieldOffsets![fieldNum], fieldNum);
}