DC only AEAP-ports the most recently seen contact if the key is shared

[iequidoo]

If we have two contacts with the same key in a verified group and then someone writes to this group with the same key from a third address, currently Delta Chat will only AEAP-port the most recently seen contact.

Probably in such a case it's better not to port any contact at all. We don't know which one to port. If we port both (i.e. replace them with the new one), then it's a question why they both exist before (probably because the key is shared). Sharing a key isn't a common scenario, if we want AEAP to work in this case too, we better add an additional attribute to the Autocrypt header, smth like setup-id.