sepa attachments migration fix

Sometimes sepa file could have been detached
from the corresponding payment order.

account_banking_sepa_credit_transfer/migrations/8.0.0.3/post-migration.py

@@ -39,6 +39,8 @@ def migrate(cr, version):
         ''')
 
     for sepa_file in cr.dictfetchall():
+        if not sepa_file['payment_order_id']:
+            continue
         filename = 'sct_%s.xml' % sepa_file['reference'].replace('/', '-')
         pool['ir.attachment'].create(
             cr, SUPERUSER_ID, {