[dlive, enhancement] TypeError: 'NoneType' object is not subscriptable when stream is offline

[vedranmiletic]

Checklist

• I'm reporting a broken site support
• I've verified that I'm running youtube-dl version 2019.08.13
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar issues including closed ones

Verbose log

$ youtube-dl -v https://dlive.tv/PewDiePie 
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', 'https://dlive.tv/PewDiePie']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2019.08.13
[debug] Python version 3.5.7 (CPython) - SunOS-5.11-i86pc-i386-64bit-ELF
[debug] exe versions: none
[debug] Proxy map: {}
Creating Plan (Solver setup): \[dlive:stream] PewDiePie: Downloading JSON metadata
Traceback (most recent call last):
  File "/export/home/vedranm/.local/bin/youtube-dl", line 10, in <module>
    sys.exit(main())
  File "/export/home/vedranm/.local/lib/python3.5/site-packages/youtube_dl/__init__.py", line 474, in main
    _real_main(argv)
  File "/export/home/vedranm/.local/lib/python3.5/site-packages/youtube_dl/__init__.py", line 464, in _real_main
    retcode = ydl.download(all_urls)
  File "/export/home/vedranm/.local/lib/python3.5/site-packages/youtube_dl/YoutubeDL.py", line 2010, in download
    url, force_generic_extractor=self.params.get('force_generic_extractor', False))
  File "/export/home/vedranm/.local/lib/python3.5/site-packages/youtube_dl/YoutubeDL.py", line 796, in extract_info
    ie_result = ie.extract(url)
  File "/export/home/vedranm/.local/lib/python3.5/site-packages/youtube_dl/extractor/common.py", line 530, in extract
    ie_result = self._real_extract(url)
  File "/export/home/vedranm/.local/lib/python3.5/site-packages/youtube_dl/extractor/dlive.py", line 80, in _real_extract
    title = livestream['title']
TypeError: 'NoneType' object is not subscriptable

Description

It would be nice if youtube-dl would print a neat error message instead of this error when the requested DLive stream is offline.