js_to_json comment parsing is removing a comma

[tiagoad]

Checklist

• I'm reporting a broken site support issue
• I've verified that I'm running youtube-dl version 2020.03.24
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Description

I have found that on the git version, in certain conditions, the js_to_json parser will remove a comma from the data, resulting in unparsable json.

This can be seen on the link https://www.rtp.pt/play/p1039/odisseia, where the JS

          id: "player_prog",
          fileKey: "/nas2.share/h264/512x384/odisseia/odisseia_1_20130120.mp4",
          file : "https://streaming-ondemand.rtp.pt/nas2.share/h264/512x384/odisseia/index.m3u8?tlm=hls&streams=odisseia_1_20130120.mp4.m3u8:1024",
                                  seekBarThumbnailsLoc: '//cdn-images.rtp.pt/multimedia/screenshots/',
                      adsType: 'dfp',
          subadUnit: 'Play',
          streamType:"ondemand",
          googleCast: true,
          //extraSettings: { googleCastReceiverAppId:'1A6F2224', skin:'s3',  skinAccentColor: '0073FF'},
          extraSettings: { googleCastReceiverAppId:'1A6F2224'},
          mediaType: "video",
          poster: "https://cdn-images.rtp.pt/EPG/imagens/29649_34099_15556.png?v=3&w=1170",
          modules: [{ name: 'RTPFavIcon', bucket: '1' }]
        }

turns into JSON

{
          "id": "player_prog",
          "fileKey": "/nas2.share/h264/512x384/odisseia/odisseia_1_20130120.mp4",
          "file" : "https://streaming-ondemand.rtp.pt/nas2.share/h264/512x384/odisseia/index.m3u8?tlm=hls&streams=odisseia_1_20130120.mp4.m3u8:1024",
                                  "seekBarThumbnailsLoc": "//cdn-images.rtp.pt/multimedia/screenshots/",
                      "adsType": "dfp",
          "subadUnit": "Play",
          "streamType":"ondemand",
          "googleCast": true

          "extraSettings": { "googleCastReceiverAppId":"1A6F2224"},
          "mediaType": "video",
          "poster": "https://cdn-images.rtp.pt/EPG/imagens/29649_34099_15556.png?v=3&w=1170",
          "modules": [{ "name": "RTPFavIcon", "bucket": "1" }]
        }

The comma after the googleCast key was removed, resulting in an error.

This is caused by this line of code:

youtube-dl/youtube_dl/utils.py

Line 2422 in ead467a

{comment}|,(?={skip}[\]}}])|