Bug 23242: Fix insert of Z3950 servers with strict SQL modes

Bug 23242: Fix insert of Z3950 servers with strict SQL modes

If strict SQL modes are set, the insertion of a new Z3950 server can
fail.

DBIx::Class::Storage::DBI::_dbh_execute(): Incorrect integer value: ''
for column 'checked' at row 1 at
/home/vagrant/kohaclone/admin/z3950servers.pl line 82

Using Koha::Z3950Servers fixes the issue (handled from
Koha::Object->store)

Test plan:
- Turn the strict SQL modes on (config strict_sql_modes)
- Create a new Z3950 server filling only the mandatory fields.
=> Without this patch you will get the failure, with this patch applied
the server will be inserted sucessfully
- Delete it
=> No regression should be found
- Search for servers
=> No regression should be found (the search is a start-with, LIKE "$pattern%")

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>