Clean unread mails count when last subscriber calls Unsubscribe()
Clean unread mails count when last subscriber calls Unsubscribe()

This will fix mail-notification.py that fails since patch:
e817d77310d94c5e1aec42a848eacededd82f01c.

mlundblad/telepathy-gabble,jku/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble,mlundblad/telepathy-gabble