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_parse_handle_partition_or_eof(MXFContext *mxf)
{
    return mxf->parsing_backward ? mxf_seek_to_previous_partition(mxf) : 1;
}

static int mxf_parse_handle_partition_or_eof(MXFContext *mxf)
{
    return mxf->parsing_backward ? mxf_seek_to_previous_partition(mxf) : 1;
}
