demux/demux_lavf: pass-through mime_type

This fixes HLS playback. After FFmpeg@954d16f check is strict as per
RFC8216 requirement and demuxer need to have this information to work
properly.

demux/demux_lavf.c

@@ -472,6 +472,7 @@ static int lavf_check_file(demuxer_t *demuxer, enum demux_check check)
                     check <= DEMUX_CHECK_REQUEST ? priv->filename : "",
         .buf_size = 0,
         .buf = av_mallocz(PROBE_BUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE),
+        .mime_type = lavfdopts->allow_mimetype ? mime_type : NULL,
     };
     if (!avpd.buf)
         return -1;