avformat/movenc: Write version 2 of audio atom if channels is not known

The version 1 needs the channel count and would divide by 0
Fixes: division by 0
Fixes: fpe_movenc.c_1108_1.ogg
Fixes: fpe_movenc.c_1108_2.ogg
Fixes: fpe_movenc.c_1108_3.wav

Found-by: #CHEN HONGXU# <HCHEN017@e.ntu.edu.sg>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
static int mov_write_mdat_tag(AVIOContext *pb, MOVMuxContext *mov)
{
    avio_wb32(pb, 8);    // placeholder for extended size field (64 bit)
    ffio_wfourcc(pb, mov->mode == MODE_MOV ? "wide" : "free");

    mov->mdat_pos = avio_tell(pb);
    avio_wb32(pb, 0); /* size placeholder*/
    ffio_wfourcc(pb, "mdat");
    return 0;
}

static int mov_write_mdat_tag(AVIOContext *pb, MOVMuxContext *mov)
{
    avio_wb32(pb, 8);    // placeholder for extended size field (64 bit)
    ffio_wfourcc(pb, mov->mode == MODE_MOV ? "wide" : "free");

    mov->mdat_pos = avio_tell(pb);
    avio_wb32(pb, 0); /* size placeholder*/
    ffio_wfourcc(pb, "mdat");
    return 0;
}
