Improve the matching of the return value of `Connection::fetch` in `Connection::fetchone`

[antaljanosbenjamin]

Connection::fetch will only return two combinations:

• (Some(row), None): when a new row is obtained
• (None, Some(has_more)) when there is no more records

In contrast what we are expecting is:

• (Some(row), None)
• (Some(row), Some(has_more))
• (None, _)

These sohuld be syncronized.