Bug 31112: (follow-up) Don't return "on_reserve" when there are 0 possible holds

Bug 31112: (follow-up) Don't return "on_reserve" when there are 0 possible holds

It's possible that there could be 0 possible reserves, for example
when the hold has already been filled, thus the check would fail as
the item count can never be less than 0.

Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 507edad61f16d99d4fba4ce343cbaa6eb3950957)

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