Bug 7311: Only run analytics code if analytics are enabled

Bug 7311: Only run analytics code if analytics are enabled

With the addition of the code from Bug 5528 (easy analytic record workflows),
UNIMARC 461$0 and MARC21/NORMARC 773$0 have special meanings. When you import
a record that uses those subfields for different data, you will get an error
in /cataloguing/additem.pl. A check should be added to be sure that
EasyAnalyticalRecords is enabled before trying to handle the 461$0/773$0 as
bib numbers for analytics.

Thanks to Frère Sébastien Marie for spotting this issue.

Signed-off-by: Frère Sébastien Marie <semarie-koha@latrappe.fr>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>