base: make Entity_sendEmail raise early for missing email addresses

on python2, this sends an email with address like "Name <None>", on
python3 this fails with an error like this:

  Module script, line 15, in Entity_sendEmail
   - <PythonScript at /portal_2664097758140587659/Entity_sendEmail used for /portal_2664097758140587659/person_module/20241227-13AB7>
   - Line 15
    from_url = formataddr((sender.hasTitle() and sender.getTitle(), sender.getDefaultEmailText()))
  Module email.utils, line 92, in formataddr
    address.encode('ascii')

better to fail early in such a case