Bug 21170: Remove "isn't numeric in numeric eq (==)" warnings in MARCdetail

Bug 21170: Remove "isn't numeric in numeric eq (==)" warnings in MARCdetail

Easily removed switching the two conditions.

Test plan:
Hit catalogue/MARCdetail.pl?biblionumber=1
=> Without this patch you will see in the log warnings like
  Argument "ddc" isn't numeric in numeric eq (==) at /home/vagrant/kohaclone/catalogue/MARCdetail.pl line 277.
=> With this patch applied the warnings do no longer appear

Signed-off-by: Pierre-Marc Thibault <pierre-marc.thibault@inLibro.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>