Bug 24361: (bug 24217 follow-up) Fix several warnings in C4 modules

Bug 24361: (bug 24217 follow-up) Fix several warnings in C4 modules

With bug 24217 pushed, lot of warnings appears during the tests are run.
Most of them are "Use of uninitialized value in "

Test plan:
Take a look at the output of run 1049
https://jenkins.koha-community.org/job/Koha_Master_D9/1049/consoleFull

Most of the warnings from this run will be removed by this patch

At least 2 are not fixed:
Use of uninitialized value in numeric eq (==) at /kohadevbox/koha/C4/Reserves.pm line 791.
t/db_dependent/Items_DelItemCheck.t => see 23463

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>