AttributeError: 'FFMPEG_AudioReader' object has no attribute 'proc'

Exception ignored in: <bound method FFMPEG_AudioReader.__del__ of <moviepy.audio.io.readers.FFMPEG_AudioReader object at 0x7fc339261cf8>>
Traceback (most recent call last):
  File "/home/vagrant/.tox/py36/lib/python3.6/site-packages/moviepy/audio/io/readers.py", line 264, in __del__
    self.close()
  File "/home/vagrant/.tox/py36/lib/python3.6/site-packages/moviepy/audio/io/readers.py", line 254, in close
    if self.proc:
AttributeError: 'FFMPEG_AudioReader' object has no attribute 'proc'

Commit a3787719bed2ca4834ae6dc2f04567e4c229e81a works, 2482d139dd5514463bc1985bbcb5203250957603 fails. Latest master fails similarly as well.

I see this error littered through our test logs for a variety of file types of audio & video. If you have trouble reproducing it then I will try to be more detailed.

Only difference with master is a slight change in line numbers:

Exception ignored in: <bound method FFMPEG_AudioReader.__del__ of <moviepy.audio.io.readers.FFMPEG_AudioReader object at 0x7fcbc5e229b0>>
Traceback (most recent call last):
  File "/home/vagrant/.tox/py36/lib/python3.6/site-packages/moviepy/audio/io/readers.py", line 266, in __del__
    self.close()
  File "/home/vagrant/.tox/py36/lib/python3.6/site-packages/moviepy/audio/io/readers.py", line 256, in close
    if self.proc:
AttributeError: 'FFMPEG_AudioReader' object has no attribute 'proc'