poe plugin crashes when type is not set

[jmbredal]

2017-11-28 09:17:48,002 [ERROR jobs.jobhandler] [statuscheck xxx.xxx.xxx] Plugin nav.ipdevpoll.plugins.poe.Poe(u'xxx.xxx.xxx') reported an unhandled failure
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/twisted/internet/defer.py", line 577, in _runCallbacks
    current.result = callback(current.result, *args, **kw)
  File "/source/python/nav/ipdevpoll/jobs.py", line 222, in next_plugin
    df = defer.maybeDeferred(plugin_instance.handle)
  File "/usr/local/lib/python2.7/dist-packages/twisted/internet/defer.py", line 139, in maybeDeferred
    result = f(*args, **kw)
  File "/usr/local/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1237, in unwindGenerator
    return _inlineCallbacks(None, gen, Deferred())
--- <exception caught here> ---
  File "/usr/local/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1099, in _inlineCallbacks
    result = g.send(result)
  File "/source/python/nav/ipdevpoll/plugins/poe.py", line 38, in handle
    if self.netbox.type.vendor.id == 'cisco':
exceptions.AttributeError: 'NoneType' object has no attribute 'vendor'

[lunkwill42]

This looks like a duplicate of #1616