Error on delivery email should not break dataset creation process

[acorbi]

While creating a new dataset on data.opendevelopmentmekong.net with user admin, following error is raise when trying to send email notification:

    2016-01-07 20:35:02,009 DEBUG [ckanext.issues.controller.notification] send_email to None None
    2016-01-07 20:35:02,031 ERROR [ckan.lib.mailer] SMTPRecipientsRefused({None: (501, '5.1.3 Bad recipient address syntax')},)
     Traceback (most recent call last):
      File "./ckan/lib/mailer.py", line 82, in _mail_recipient
         smtp_connection.sendmail(mail_from, [recipient_email], msg.as_string())
      File "/usr/lib/python2.7/smtplib.py", line 735, in sendmail
        raise SMTPRecipientsRefused(senderrs)
    SMTPRecipientsRefused: {None: (501, '5.1.3 Bad recipient address syntax')}
    Traceback (most recent call last):
      File "/usr/local/lib/python2.7/dist-packages/ckanext/issues/controller/notification.py", line 87, in send_email
        mail_recipient(contact_name, contact_email,"Dataset issue",email_msg, headers=headers)
      File "./ckan/lib/mailer.py", line 95, in mail_recipient
        g.site_title, g.site_url, subject, body, headers=headers)
      File "./ckan/lib/mailer.py", line 88, in _mail_recipient
        raise MailerException(msg)

Investigate the origin of the error and improve code so exception gets caught and dataset creation process does not get interrupted with Error 500