DecDaysCode
procedure DecDaysCode (const Key : TKey; var Code : TCode);

DecDaysCode reduces the internal "days count" value by one and returns the modified code as the Code parameter.

Key must be the same key that was used to create the code or the code is considered invalid.

This routine is defined in the OnGuard unit. (as of 1.15 this routine has been moved to the OgUtil unit)