[utils] js_to_json can't handle scientific notations (was: [twitch:clips] JSONDecodeError for certain clips)

[s104346]

• I've verified and I assure that I'm running youtube-dl 2017.11.15

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• Searched the bugtracker for similar issues including closed ones

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• Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
• Feature request (request for a new functionality)
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If the purpose of this issue is a bug report, site support request or you are not completely sure provide the full verbose output as follows:

Add the -v flag to your command line you run youtube-dl with (youtube-dl -v <your command line>), copy the whole output and insert it here. It should look similar to one below (replace it with your log inserted between triple ```):

$ python -m youtube_dl --verbose https://clips.twitch.tv/CarelessZealousKangarooNerfBlueBlaster
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--verbose', 'https://clips.twitch.tv/CarelessZealousKangarooNerfBlueBlaster']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2017.11.15
[debug] Git HEAD: f610dbb05
[debug] Python version 3.6.3 - Linux-4.12.13-1-ARCH-x86_64-with-arch
[debug] exe versions: ffmpeg 3.4, ffprobe 3.4, rtmpdump 2.4
[debug] Proxy map: {}
[twitch:clips] CarelessZealousKangarooNerfBlueBlaster: Downloading webpage
ERROR: CarelessZealousKangarooNerfBlueBlaster: Failed to parse JSON  (caused by JSONDecodeError("Expecting ',' delimiter: line 38 column 78 (char 2178)",)); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
Traceback (most recent call last):
  File "/tmp/youtube-dl/youtube_dl/extractor/common.py", line 686, in _parse_json
    return json.loads(json_string)
  File "/usr/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.6/json/decoder.py", line 355, in raw_decode
    obj, end = self.scan_once(s, idx)
json.decoder.JSONDecodeError: Expecting ',' delimiter: line 38 column 78 (char 2178)
Traceback (most recent call last):
  File "/tmp/youtube-dl/youtube_dl/extractor/common.py", line 686, in _parse_json
    return json.loads(json_string)
  File "/usr/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.6/json/decoder.py", line 355, in raw_decode
    obj, end = self.scan_once(s, idx)
json.decoder.JSONDecodeError: Expecting ',' delimiter: line 38 column 78 (char 2178)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/tmp/youtube-dl/youtube_dl/YoutubeDL.py", line 784, in extract_info
    ie_result = ie.extract(url)
  File "/tmp/youtube-dl/youtube_dl/extractor/common.py", line 437, in extract
    ie_result = self._real_extract(url)
  File "/tmp/youtube-dl/youtube_dl/extractor/twitch.py", line 610, in _real_extract
    video_id, transform_source=js_to_json)
  File "/tmp/youtube-dl/youtube_dl/extractor/common.py", line 690, in _parse_json
    raise ExtractorError(errmsg, cause=ve)
youtube_dl.utils.ExtractorError: CarelessZealousKangarooNerfBlueBlaster: Failed to parse JSON  (caused by JSONDecodeError("Expecting ',' delimiter: line 38 column 78 (char 2178)",)); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.

Description of your issue, suggested solution and other information

Most twitch clips work just fine, but this specific one causes problems (https://clips.twitch.tv/CarelessZealousKangarooNerfBlueBlaster).

Looking at the js/json string being parsed suggests that its segments value, which is null for all working clips including youtube-dl's test URLs, is the culprit. The original form of this line is

segments: [{"playback_offset":0,"offset":-3.885780586188048e-16,"duration":39.75000000000001,"speed":1}],

which gets transformed into

"segments": [{"playback_offset":0,"offset":-3.885780586188048"e"-16,"duration":39.75000000000001,"speed":1}],

This adds quotation marks around the exponent marker which causes the error.