Push AUD units to fix decode errors with some TS segments

[robwalch]

This PR will...

Push AUD units to fix decode errors with some TS segments

Why is this Pull Request needed?

Found TS playlists that produce a decode error in HLS.js but not in other MSE based players that push AUD units to the data they remux into fmp4.

Example decoding error:

Selected VDAVideoDecoder for video decoding, config: codec: h264, profile: h264 baseline, level: not available, alpha_mode: is_opaque, coded size: [640,360], visible rect: [0,0,640,360], natural size: [640,360], has extra data: false, encryption scheme: Unencrypted, rotation: 0°, flipped: 0, color space: {primaries:BT709, transfer:BT709, matrix:BT709, range:LIMITED}
VDA Error 4
video decode error!

Error Group: DecoderStatus
Error Code: 1
Stacktrace: media/gpu/ipc/service/vda_video_decoder.cc:919

Error Group: PipelineStatus
Error Code: 3
Stacktrace: media/renderers/video_renderer_impl.cc:591
Caused by:
  Error Group:  DecoderStatus
  Error Code: 108
  Stacktrace: media/filters/decoder_stream.cc:192

Are there any points in the code the reviewer needs to double check?

This should not impact the playback of any TS media already supported by HLS.js.

Resolves issues:

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md