I tried simply disabling the OK button but I didn't success.
I think it's not worth spend lot of time working on this as is a very specific case: there must be no serial port on the system and no last_port in the configuration.
Nevertheless we have to solve it.
ok Marco, it's windows but you can do it ... you can do it ... you can do it ...
In this patch the simpliest solution: just display an empty list, should user try to download it gets reasonable error and an empty port is saved in config (which is safe).
73 de IZ3GME Marco