ffprobe parsing may fail for different metadata formats

[atruskie]

The line here https://github.com/QutBioacoustics/baw-audio-tools/blob/master/lib/baw-audio-tools/audio_ffmpeg.rb#L182 fails to parse output from ffprobe like:

ffprobe -sexagesimal -print_format default -show_error -show_streams -show_format "D:\TEMP\20110412_150000.wav"
ffprobe version 3.4.1 Copyright (c) 2007-2017 the FFmpeg developers
  built with gcc 7.2.0 (GCC)
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-bzlib --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-cuda --enable-cuvid --enable-d3d11va --enable-nvenc --enable-dxva2 --enable-avisynth --enable-libmfx
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
Input #0, wav, from 'D:\TEMP\20110412_150000.wav':
  Metadata:
    date            : 2007-01-01
    creation_time   : 00:50:48
    time_reference  : 0
    coding_history  : Format=PCM,Mode=STEREO,Sample frequency=44100Hz,Size of the sample=16bit ZOOM Handy Recorder H2

                    :
  Duration: 00:15:15.03, bitrate: 1411 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, 2 channels, s16, 1411 kb/s
[STREAM]
index=0
codec_name=pcm_s16le
codec_long_name=PCM signed 16-bit little-endian
profile=unknown
codec_type=audio
codec_time_base=1/44100
codec_tag_string=[1][0][0][0]
codec_tag=0x0001
sample_fmt=s16
sample_rate=44100
channels=2
channel_layout=unknown
bits_per_sample=16
id=N/A
r_frame_rate=0/0
avg_frame_rate=0/0
time_base=1/44100
start_pts=N/A
start_time=N/A
duration_ts=40353020
duration=0:15:15.034467
bit_rate=1411200
max_bit_rate=N/A
bits_per_raw_sample=N/A
nb_frames=N/A
nb_read_frames=N/A
nb_read_packets=N/A
DISPOSITION:default=0
DISPOSITION:dub=0
DISPOSITION:original=0
DISPOSITION:comment=0
DISPOSITION:lyrics=0
DISPOSITION:karaoke=0
DISPOSITION:forced=0
DISPOSITION:hearing_impaired=0
DISPOSITION:visual_impaired=0
DISPOSITION:clean_effects=0
DISPOSITION:attached_pic=0
DISPOSITION:timed_thumbnails=0
[/STREAM]
[FORMAT]
filename=D:\TEMP\20110412_150000.wav
nb_streams=1
nb_programs=0
format_name=wav
format_long_name=WAV / WAVE (Waveform Audio)
start_time=N/A
duration=0:15:15.034467
size=161412914
bit_rate=1411207
probe_score=99
TAG:date=2007-01-01
TAG:creation_time=00:50:48
TAG:time_reference=0
TAG:coding_history=Format=PCM,Mode=STEREO,Sample frequency=44100Hz,Size of the sample=16bit ZOOM Handy Recorder H2


[/FORMAT]

Parsing this sort of output results in the following exception:

The error was:

Error: no implicit conversion from nil to integer

Backtrace: /home/ubuntu/bioacoustics/workers/baw-workers_production/vendor/bundle/ruby/2.3.0/bundler/gems/baw-audio-tools-d8b0f4e2796c/lib/baw-audio-tools/audio_ffmpeg.rb:182:in `[]'
/home/ubuntu/bioacoustics/workers/baw-workers_production/vendor/bundle/ruby/2.3.0/bundler/gems/baw-audio-tools-d8b0f4e2796c/lib/baw-audio-tools/audio_ffmpeg.rb:182:in `block in parse_ffprobe_output'
/home/ubuntu/bioacoustics/workers/baw-workers_production/vendor/bundle/ruby/2.3.0/bundler/gems/baw-audio-tools-d8b0f4e2796c/lib/baw-audio-tools/audio_ffmpeg.rb:176:in `each'
/home/ubuntu/bioacoustics/workers/baw-workers_production/vendor/bundle/ruby/2.3.0/bundler/gems/baw-audio-tools-d8b0f4e2796c/lib/baw-audio-tools/audio_ffmpeg.rb:176:in `parse_ffprobe_output'
/home/ubuntu/bioacoustics/workers/baw-workers_production/vendor/bundle/ruby/2.3.0/bundler/gems/baw-audio-tools-d8b0f4e2796c/lib/baw-audio-tools/audio_base.rb:121:in `info_ffmpeg'
/home/ubuntu/bioacoustics/workers/baw-workers_production/vendor/bundle/ruby/2.3.0/bundler/gems/baw-audio-tools-d8b0f4e2796c/lib/baw-audio-tools/audio_base.rb:94:in `info'
/home/ubuntu/bioacoustics/workers/baw-workers_production/lib/baw-workers/file_info.rb:21:in `audio_info'