[QSqlQuery] misbehavior of seek in special query positions

When QSqlQuery::at() == QSql::BeforeFirstRow and seek(1, true) (seek to
next record) is called the expected result is go to first row.
When QSqlQuery::at() == QSql::AfterLastRow and seek(-1, true) (seek to
previous record) is called the expected result is go to last row.

But in all cases the first and last are skipped.

Change-Id: I584138b3d397ce1c790bf89688ee92289a99611c
Reviewed-by: Mark Brand <mabrand@mabrand.nl>