[TVer] improper file extension for some videos

[ghost]

Checklist

• I'm reporting a broken site support
• I've verified that I'm running youtube-dl version 2021.03.03
• 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 --ignore-config -v --hls-prefer-native -f worst https://tver.jp/corner/f0069218 
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--ignore-config', '-v', '--hls-prefer-native', '-f', 'worst', 'https://tver.jp/corner/f0069218']
[debug] Encodings: locale UTF-8, fs utf-8, out utf-8, pref UTF-8
[debug] youtube-dl version 2021.03.03
[debug] Python version 3.9.2 (CPython) - macOS-10.12.6-x86_64-i386-64bit
[debug] exe versions: ffmpeg N-101345-g3072438, ffprobe N-101345-g3072438, phantomjs 2.1.1
[debug] Proxy map: {}
[TVer] Downloading JSON metadata
[TVer] f0069218: Downloading JSON metadata
[FujiTVFODPlus7] 2359810114: Downloading m3u8 information
[debug] Invoking downloader on 'https://fod-plus7.hls.wseod.stream.ne.jp/www08/fod-plus7/_definst_/mp4:video/01234/2359/2359810114me1104e46.mp4/chunklist.m3u8'
[hlsnative] Downloading m3u8 manifest
[hlsnative] Total fragments: 180
[download] Destination: #114「鉄拳7」-2359810114.m3u8
[download] 100% of 76.40MiB in 00:32
[debug] ffmpeg command line: ffprobe -show_streams 'file:#114「鉄拳7」-2359810114.m3u8'
[ffmpeg] Fixing malformed AAC bitstream in "#114「鉄拳7」-2359810114.m3u8"
[debug] ffmpeg command line: ffmpeg -y -loglevel repeat+info -i 'file:#114「鉄拳7」-2359810114.m3u8' -c copy -f mp4 -bsf:a aac_adtstoasc 'file:#114「鉄拳7」-2359810114.temp.m3u8'
$ ls -1
#114「鉄拳7」-2359810114.m3u8

Description

File extension should be 'mp4' but youtube-dl improperly generates 'm3u8' for videos under https://tver.jp/cx .