ISKeyValueList.GetString; if value is a Double and NAN it now returns a blank string

The Business Layer function ISKeyValueList.GetString was returning "NAN" if the value stored is a Double value type with a value of NAN (Not a Number).

This has been changed so a blank string is returned.

This has the effect of storing a blank text value in User0 to User9 fields in the database for User Defined data. Search forms will then display a blank instead of NAN, e.g. on the External Party Search form.

Note, existing User0 to User9 fields stored in the database will not immediately change.