Fix registration for invited persons without email

aleksis/core/schema/person.py

@@ -636,6 +636,7 @@ class SendAccountRegistrationMutation(PersonAddressMutationMixin, graphene.Mutat
         # Create person if no invitation is given or if invitation isn't linked to a person
         if invitation and invitation.person:
             person = invitation.person
+            person.email = email
             person.user = user
             person.save()
         else: