Problem:
- `pos.cursor()` receives a table contains `row` and `col` as arguments,
but `pos:to_cursor` returns `row` and `col` directly
without wrapping them in a table.
- `pos.mark()`/`pos:to_mark` can already handle unpacked `row` `col`.
Solution:
Make `pos:to_cursor()` return a `row` and `col` in a table.
f79999270e
