cve-check: close cursors as soon as possible

cve-check: close cursors as soon as possible

We can have multiple processes reading the database at the same time, and
cursors only release their locks when they're garbage collected.

This might be the cause of random sqlite errors on the autobuilder, so
explicitly close the cursors when we're done with them.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
(cherry picked from commit 5d2e90e4a58217a943ec21140bc2ecdd4357a98a)
Signed-off-by: Steve Sakoman <steve@sakoman.com>