avformat/mov: Fix DoS in read_tfra()

Fixes: Missing EOF check in loop
No testcase

Found-by: Xiaohei and Wangchu from Alibaba Security Team
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
static int mov_read_avss(MOVContext *c, AVIOContext *pb, MOVAtom atom)
{
    return mov_read_extradata(c, pb, atom, AV_CODEC_ID_AVS);
}

static int mov_read_avss(MOVContext *c, AVIOContext *pb, MOVAtom atom)
{
    return mov_read_extradata(c, pb, atom, AV_CODEC_ID_AVS);
}
