VTT subtitles cannot be processed

[nnnytt]

Summary of the bug: VTT subtitles are processed as empty.

How to reproduce:

ffprobe version 5.1.2 Copyright (c) 2007-2022 the FFmpeg developers
  built with Apple clang version 14.0.0 (clang-1400.0.29.202)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/5.1.2_1 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
  libavutil      57. 28.100 / 57. 28.100
  libavcodec     59. 37.100 / 59. 37.100
  libavformat    59. 27.100 / 59. 27.100
  libavdevice    59.  7.100 / 59.  7.100
  libavfilter     8. 44.100 /  8. 44.100
  libswscale      6.  7.100 /  6.  7.100
  libswresample   4.  7.100 /  4.  7.100
  libpostproc    56.  6.100 / 56.  6.100
Input #0, webvtt, from '01.vtt':
  Duration: N/A, bitrate: N/A
  Stream #0:0: Subtitle: webvtt

Any try to render this subtitle file with lead to empty file. I tried to convert to SRT with some other tool and then it works fine.

[zebul666]

I can confirm that bug

It seems to be a problem with the STYLEs at the start of the file, because removing all the STYLE blocks, gives you an output, after all.

But this also gives wrong carriage return for multi-lines if output is srt. For example, with 02.vtt this gives:

1
00:00:04,640 --> 00:00:08,520
Detta har hänt:^M
det är midsommarafton 1973.

[...]

[August Wikerfors]

Duplicate of #8684 or #9064