Deleting email address or phone of CiviMail recipient causes job to hang

This is a side-effect of CRM-18345 [Deleting an email address deletes any mailing events related to it, and the contact]

One impact of CRM-18345 is deleting an email address no longer deletes rows in civicrm_mailing_recipient, but rather sets the email_id to NULL.

Similarly deleting a phone sets phone_id to NULL.

So the Mailing Job software needs to handle rows where BOTH email_id and phone_id are NULL.

I'm supplying a patch that hadles this case by ignoring such rows.