Handle EVENT_STATE_CHANGED with no new_state in graphite

I noticed some events that came in with new_state=None. Make graphite
defensive about this.

homeassistant/components/graphite.py

@@ -110,7 +110,7 @@ class GraphiteFeeder(threading.Thread):
                 self._queue.task_done()
                 return
             elif (event.event_type == EVENT_STATE_CHANGED and
-                  'new_state' in event.data):
+                  event.data.get('new_state')):
                 self._report_attributes(event.data['entity_id'],
                                         event.data['new_state'])
             self._queue.task_done()

tests/components/test_graphite.py

@@ -171,7 +171,8 @@ class TestGraphite(unittest.TestCase):
                 return self.gf._quit_object
             elif runs:
                 runs.append(1)
-                return mock.MagicMock(event_type='somethingelse')
+                return mock.MagicMock(event_type='somethingelse',
+                                      data={'new_event': None})
             else:
                 runs.append(1)
                 return event