- The driver being used for PostgreSQL doesn't handle interleaved
queries (you start a query, read some rows and start another query while
you didn't finish that query yet), this is the case with using
`.Iterate` from XORM.
- Switch to a variant of what exist in the current codebase of
`db.Iterate`, which is a simple buffered iteration and doesn't keep
queries open, which allow other database operations to happen.
- Unit test added. This doesn't cover that postgres does not error on
this case, as this is not run with a postgres database.
- Resolves#5696
(cherry picked from commit 459ab11a8a)
