sqlops: reset the result container before new query is executed

- it was lost in commit 9b62514b4a90e169c9126b7bda6d87cc4c213ad2
- reported by Jonas Böttner

(cherry picked from commit 864127e6e02144c40c138d6921862b1512d01c66)
(cherry picked from commit 954fe136964296836113f5187f9cde91b197a567)