NZ CCCFA Loss Formula 1; updated logic to handle where no payment has yet been due

During the period between when the Loan opened and when the first payment is due the "d" variable in the formula was always "0".

Technically the CCCF Regulations state "d= the number of days since the last payment due date" - and as no payment has been due could be said to be 0.

However, "d' is now calculated as if a payment was due when opened - so that the formula looks correct.