Subsync erroring out with "max() arg is an empty sequence".

Environment (please complete the following information):

• OS: Ubuntu 18.04 LTS
• python version: Python 2.7.17
• subsync version: subsync 0.3.4

Describe the bug
The sync process fails with an error ValueError: max() arg is an empty sequence

To Reproduce
subsync "vid.mp4" -i sub1.srt -o sub2.srt

Expected behavior
The process should succeed.

Output

INFO:subsync.subsync:extracting speech segments from reference 'vid.mp4'...
INFO:subsync.speech_transformers:Checking video for subtitles stream...
INFO:subsync.speech_transformers:Video file appears to lack subtitle stream
100%|█████████▉| 7687.72266667/7687.723 [01:33<00:00, 81.91it/s]
INFO:subsync.subsync:...done
INFO:subsync.subsync:extracting speech segments from subtitles 'sub1.srt'...
INFO:subsync.subtitle_parser:detected encoding: UTF-8
INFO:subsync.subsync:...done
INFO:subsync.subsync:computing alignments...
Traceback (most recent call last):
  File "/home/user/.local/bin/subsync", line 11, in <module>
    load_entry_point('subsync==0.3.4', 'console_scripts', 'subsync')()
  File "/home/user/.local/lib/python2.7/site-packages/subsync/subsync.py", line 207, in main
    return run(args)
  File "/home/user/.local/lib/python2.7/site-packages/subsync/subsync.py", line 106, in run
    srt_pipes,
  File "/home/user/.local/lib/python2.7/site-packages/sklearn/base.py", line 467, in fit_transform
    return self.fit(X, y, **fit_params).transform(X)
  File "/home/user/.local/lib/python2.7/site-packages/subsync/aligners.py", line 77, in transform
    (score, offset), subpipe = max(scores)
ValueError: max() arg is an empty sequence

Test case
vid.zip

Additional context
--

The failure is raised in subsync/aligners.py at line 77 during the sklearn fit_transform path; start there and reproduce with the command and attached vid.zip. Confirm the same input no longer aborts during computing alignments and that the expected output subtitle file is produced.