void ff_clean_intra_table_entries(MpegEncContext *s)
{
    int wrap = s->b8_stride;
    int xy = s->block_index[0];

    s->dc_val[0][xy           ] =
    s->dc_val[0][xy + 1       ] =
    s->dc_val[0][xy     + wrap] =
    s->dc_val[0][xy + 1 + wrap] = 1024;
    /* ac pred */
    memset(s->ac_val[0][xy       ], 0, 32 * sizeof(int16_t));
    memset(s->ac_val[0][xy + wrap], 0, 32 * sizeof(int16_t));
    if (s->msmpeg4_version>=3) {
        s->coded_block[xy           ] =
        s->coded_block[xy + 1       ] =
        s->coded_block[xy     + wrap] =
        s->coded_block[xy + 1 + wrap] = 0;
    }
    /* chroma */
    wrap = s->mb_stride;
    xy = s->mb_x + s->mb_y * wrap;
    s->dc_val[1][xy] =
    s->dc_val[2][xy] = 1024;
    /* ac pred */
    memset(s->ac_val[1][xy], 0, 16 * sizeof(int16_t));
    memset(s->ac_val[2][xy], 0, 16 * sizeof(int16_t));

    s->mbintra_table[xy]= 0;
}

The product dereferences a pointer that it expects to be valid but is NULL.