Bug 30483: Make issues.borrowernumber and itemnumber NOT NULL

Bug 30483: Make issues.borrowernumber and itemnumber NOT NULL

Note: This change does NOT apply to old_issues, where constraints
may result in nullifying these columns.

Test plan:
Run dbrev.
Try checkout, checkin.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 1f44891fd835080133fa1a73634ced0e68b96892)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>