RuntimeError when making two teams without contact addresses members of one another

[Guilherme Salgado]

To reproduce, do the following:
1. http://launchpad.dev/~guadamen/+addmember and add 'admins' there
2. http://launchpad.dev/~admins/+addmember and add 'guadamen' there
3. http://launchpad.dev/~admins/+invitation/guadamen and accept
4. http://launchpad.dev/~guadamen/+invitation/admins and accept as well

These are the interesting bits of the traceback:
Traceback (innermost last):

    * Module zope.publisher.publish, line 138, in publish
    * Module canonical.launchpad.webapp.publication, line 333, in callObject
      return mapply(ob, request.getPositionalArguments(), request)
    * Module zope.publisher.publish, line 113, in mapply
      __traceback_info__: <security proxied canonical.launchpad.browser.person.TeamInvitationView instance at 0xb4b274c>
    * Module zope.publisher.publish, line 119, in debug_call
    * Module canonical.launchpad.webapp.publisher, line 224, in __call__
      self.initialize()
    * Module canonical.launchpad.webapp.launchpadform, line 104, in initialize
      self.form_result = action.success(data)
    * Module zope.formlib.form, line 569, in success
    * Module canonical.launchpad.browser.person, line 434, in accept_action
      member.acceptInvitationToBeMemberOf(
    * Module canonical.launchpad.database.person, line 1226, in acceptInvitationToBeMemberOf
      reviewercomment=comment)
    * Module canonical.launchpad.database.teammembership, line 297, in setStatus
      self._sendStatusChangeNotification(old_status)
    * Module canonical.launchpad.database.teammembership, line 311, in _sendStatusChangeNotification
      member_email = contactEmailAddresses(member)
    * Module canonical.launchpad.helpers, line 222, in contactEmailAddresses
      contactAddresses = contactEmailAddresses(member)
...
    * Module canonical.launchpad.helpers, line 222, in contactEmailAddresses
      contactAddresses = contactEmailAddresses(member)

RuntimeError: maximum recursion depth exceeded