The poe plugin still crashes on devices that have no set type

[lunkwill42]

The same issue as described in #1616 occurs further down in the plugin code. There is also a similar issue in the POEGroup shadow handling code. This causes the statuscheck job to fail. Traceback as follows:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 382, in callback
    self._startRunCallbacks(result)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 490, in _startRunCallbacks
    self._runCallbacks()
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 577, in _runCallbacks
    current.result = callback(current.result, *args, **kw)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1155, in gotResult
    _inlineCallbacks(r, g, deferred)
--- <exception caught here> ---
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1099, in _inlineCallbacks
    result = g.send(result)
  File "/usr/lib/python2.7/dist-packages/nav/ipdevpoll/plugins/poe.py", line 55, in handle
    self._process_ports(ports, port_ifindices)
  File "/usr/lib/python2.7/dist-packages/nav/ipdevpoll/plugins/poe.py", line 74, in _process_ports
    self._update_port(netbox, index, row, ifindices.get(index))
  File "/usr/lib/python2.7/dist-packages/nav/ipdevpoll/plugins/poe.py", line 86, in _update_port
    if not ifindex and self.netbox.type.vendor.id == 'hp':
exceptions.AttributeError: 'NoneType' object has no attribute 'vendor'