Account Calculation; now validates Startup Interest Period

The Account Calculation Business Layer object now validates the Startup Interest Period is valid before performing a calculation.

Previously, if the period was blank the calculation proceeded, with the startup end date as the date the Account was opened. Now an error is returned.

In addition the finAccountCalc.StartupInterestToDateResolved function will return Nothing if the Interest Period is blank or invalid. Again, previously this would return the date the Account was opened.