fix: Don't unblock chat on possibly wrongly assigned outgoing encrypted 1:1 message

[iequidoo]

Probably needs a test.

[iequidoo]

I have no idea how to improve this. If we have multiple key-contacts with the given address, we need to assign the message to one of them and we now prefer to choose accepted contacts. But anyway we may select a blocked contact, in this case assigning the message, but not unblocking the chat, looks like a lesser harm.