Niconicolive download does not work with --proxy

[fireattack]

Checklist

• I'm reporting a broken site support
• I've verified that I'm running youtube-dl version 2020.12.14
• 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

G:\_temp\youtube-dl (animelover1984)>py -m youtube_dl --ignore-config -u *** -p *** https://live.nicovideo.jp/watch/lv331953159 --proxy socks5://localhost:1080 --verbose
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--ignore-config', '-u', 'PRIVATE', '-p', 'PRIVATE', 'https://live.nicovideo.jp/watch/lv331953159', '--proxy', 'socks5://localhost:1080', '--verbose']
[debug] Encodings: locale cp936, fs utf-8, out utf-8, pref cp936
[debug] youtube-dl version 2020.12.14
[debug] Git HEAD: 458e7fd52
[debug] Python version 3.8.7 (CPython) - Windows-7-6.1.7601-SP1
[debug] exe versions: ffmpeg 2021-03-28-git-8b2bde0494-full_build-www.gyan.dev, ffprobe 2021-03-28-git-8b2bde0494-full_build-www.gyan.dev, rtmpdump 2.3
[debug] Proxy map: {'http': 'socks5://localhost:1080', 'https': 'socks5://localhost:1080'}
[NiconicoLive] Logging in
[NiconicoLive] lv331953159: Downloading webpage
[NiconicoLive] Detected post-March 2019 HLS-based stream

Description

As soon as I use a proxy parameter, it's just stuck at "Detected post-March 2019 HLS-based stream" forever.