telepathy: Only create PersonContact for valid IM contacts in createContactsBuilder
telepathy: Only create PersonContact for valid IM contacts in createContactsBuilder

If some stale IMAddresses were left in the DB (for example, after
deleting a nco:PersonContact linked to an invalid buddy, and before the
garbage collection happened), a new contact would be created for them.

matthewvogt/contactsd,matthewvogt/contactsd,matthewvogt/contactsd,matthewvogt/contactsd