avformat/mxfdec: Fix DoS issues in mxf_read_index_entry_array()

Fixes: 20170829A.mxf

Co-Author: 张洪亮(望初)" <wangchu.zhl@alibaba-inc.com>
Found-by: Xiaohei and Wangchu from Alibaba Security Team
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
static int mxf_read_sequence(void *arg, AVIOContext *pb, int tag, int size, UID uid, int64_t klv_offset)
{
    MXFSequence *sequence = arg;
    switch(tag) {
    case 0x0202:
        sequence->duration = avio_rb64(pb);
        break;
    case 0x0201:
        avio_read(pb, sequence->data_definition_ul, 16);
        break;
        case 0x4b02:
        sequence->origin = avio_r8(pb);
        break;
    case 0x1001:
        return mxf_read_strong_ref_array(pb, &sequence->structural_components_refs,
                                             &sequence->structural_components_count);
    }
    return 0;
}

static int mxf_read_sequence(void *arg, AVIOContext *pb, int tag, int size, UID uid, int64_t klv_offset)
{
    MXFSequence *sequence = arg;
    switch(tag) {
    case 0x0202:
        sequence->duration = avio_rb64(pb);
        break;
    case 0x0201:
        avio_read(pb, sequence->data_definition_ul, 16);
        break;
        case 0x4b02:
        sequence->origin = avio_r8(pb);
        break;
    case 0x1001:
        return mxf_read_strong_ref_array(pb, &sequence->structural_components_refs,
                                             &sequence->structural_components_count);
    }
    return 0;
}
