discount with type DiscountType.PERCENTAGE are not applied to additional services

[syjer]

The discount code with % are not applied to additional services.

Example:

ticket: 1 at 10chf
additional service: 1 at 20 chf
discount at 20% applied

the UI show that it will be applied to both.

Expected price: 8chf + 16chf = 24chf

Instead the discount in the end is only applied to the ticket, thus -> 26chf.

Note: the discount must not be applied in case of donations. Only those with type: AdditionalServiceType.SUPPLEMENT

see https://github.com/alfio-event/alf.io/blob/master/src/main/java/alfio/manager/TicketReservationManager.java#L1056 .

Additionally, we have an issue with the fixed amount of discount:

If the DiscountType.FIXED_AMOUNT amount is bigger than the price of a ticket (for example: 20chf discount, but ticket cost 10chf): both in the UI and in the calculation we have a ticket cost of -10chf instead of 0chf