Deal with unsupported operand type(s) for -: 'NoneType' and 'float'

[Subarashii-no-Fansub]

Hello, Can you deal in this port with error like

  File "sushi/__main__.py", line 139, in parse_args_and_run
    run(args)
  File "sushi/__init__.py", line 635, in run
    calculate_shifts(src_stream, dst_stream, search_groups,
  File "sushi/__init__.py", line 430, in calculate_shifts
    shift = new_time - original_time
TypeError: unsupported operand type(s) for -: 'NoneType' and 'float'

Or issues like #33, #32 Thanks