If a Creditor Classification has an invalid ledger account (not blank though), the Classification Configuration form fails to load

If a Creditor Classification has an invalid ledger account (not blank though), the Classification Configuration form fails to load

Steps to reproduce:

1. In demo data, run the following sql script to "break" a classification:

UPDATE CR_Classification SET LedgerIDCreditorPurchases = 'XXXIDDOESNOTEXIST'

(Note that this is quite a possible scenario for sites upgrading from v6 to v7).

2. Go to Suppliers->Configuration->Classifications. See that form is in New Record mode when it should not be.