RowConverter::convert_columns panics when encoding Struct([])

[kawadakk]

Describe the bug
RowConverter::convert_columns panics when encoding an array of type Struct([]).

To Reproduce

#[test]
fn test_unit_struct() {
    let s = Arc::new(StructArray::new_empty_fields(5, None)) as ArrayRef;

    let sort_fields = vec![SortField::new(s.data_type().clone())];
    let converter = RowConverter::new(sort_fields).unwrap();
    let r = converter.convert_columns(&[Arc::clone(&s)]).unwrap();

    let back = converter.convert_rows(&r).unwrap();
    assert_eq!(back.len(), 1);
    assert_eq!(&back[0], &s);
}

thread 'tests::test_unit_struct' panicked at arrow-row/src/lib.rs:881:9:
assertion failed: row + 1 < self.offsets.len()

Expected behavior
Not panicking

Additional context