Song without album art prevents successful update of media status

[nohum]

Listening to a song without album or a cover art lets the MQTT update code fail because a expected key is missing within the data:

ERROR:chromecast:command CastMediaStatus(status=<MediaStatus {'metadata_type': 3, 'title': "xxx", 'series_title': None, 'season': None, 'episode': None, 'artist': 'xxx', 'album_name': '', 'album_artist': 'xxx', 'track': None, 'subtitle_tracks': {}, 'images': [MediaImage(url=None, height=0, width=0)], 'supports_pause': True, 'supports_seek': True, 'supports_stream_volume': True, 'supports_stream_mute': True, 'supports_skip_forward': False, 'supports_skip_backward': False, 'current_time': 0.591299, 'content_id': 'xxx', 'content_type': 'audio/mpeg', 'duration': 272.79200000000003, 'stream_type': 'BUFFERED', 'idle_reason': 'INTERRUPTED', 'media_session_id': 37, 'playback_rate': 1, 'player_state': 'BUFFERING', 'supported_media_commands': 207, 'volume_level': 1, 'volume_muted': False, 'media_custom_data': {}, 'media_metadata': {'metadataType': 3, 'title': "xxx", 'albumName': '', 'albumArtist': 'xxx', 'artist': 'xxx', 'images': [{'height': 0, 'width': 0}]}, 'current_subtitle_tracks': []}>) failed
Traceback (most recent call last):
  File "/home/x/PycharmProjects/chromecast-mqtt-connector/handler/adapter.py", line 204, in _worker
    self._worker_cast_media_status(item.status)
  File "/home/x/PycharmProjects/chromecast-mqtt-connector/handler/adapter.py", line 389, in _worker_cast_media_status
    image_filtered = image["url"]
KeyError: 'url'