Wrap error to allow for better error handling

[gcangussu]

Wrapping the error properly allows for real world use cases. On our case we want to add new fields to the struct and keep compatibility with the data encoded in the past.

func (data *Data) UnmarshalEnkodo(dec *enkodo.Decoder) error {
  var err error
  
  if data.OldField, err = dec.String(); err != nil {
    return err
  }

  if data.NewField, err = dec.String(); err != nil {
    if errors.Is(err, io.EOF) {
      return nil // ok, data was encoded without new field
    }
    return err
  }
}