issue #53: error out on zero sample rate
static void *find_metadata (void *wavpack_block, int desired_id, uint32_t *size)
{
    WavpackHeader *wphdr = wavpack_block;
    unsigned char *dp, meta_id, c1, c2;
    int32_t bcount, meta_bc;

    if (strncmp (wphdr->ckID, "wvpk", 4))
        return NULL;

    bcount = wphdr->ckSize - sizeof (WavpackHeader) + 8;
    dp = (unsigned char *)(wphdr + 1);

    while (bcount >= 2) {
        meta_id = *dp++;
        c1 = *dp++;

        meta_bc = c1 << 1;
        bcount -= 2;

        if (meta_id & ID_LARGE) {
            if (bcount < 2)
                break;

            c1 = *dp++;
            c2 = *dp++;
            meta_bc += ((uint32_t) c1 << 9) + ((uint32_t) c2 << 17);
            bcount -= 2;
        }

        if ((meta_id & ID_UNIQUE) == desired_id) {
            if ((bcount - meta_bc) >= 0) {
                if (size)
                    *size = meta_bc - ((meta_id & ID_ODD_SIZE) ? 1 : 0);

                return dp;
            }
            else
                return NULL;
        }

        bcount -= meta_bc;
        dp += meta_bc;
    }

    return NULL;
}

static void *find_metadata (void *wavpack_block, int desired_id, uint32_t *size)
{
    WavpackHeader *wphdr = wavpack_block;
    unsigned char *dp, meta_id, c1, c2;
    int32_t bcount, meta_bc;

    if (strncmp (wphdr->ckID, "wvpk", 4))
        return NULL;

    bcount = wphdr->ckSize - sizeof (WavpackHeader) + 8;
    dp = (unsigned char *)(wphdr + 1);

    while (bcount >= 2) {
        meta_id = *dp++;
        c1 = *dp++;

        meta_bc = c1 << 1;
        bcount -= 2;

        if (meta_id & ID_LARGE) {
            if (bcount < 2)
                break;

            c1 = *dp++;
            c2 = *dp++;
            meta_bc += ((uint32_t) c1 << 9) + ((uint32_t) c2 << 17);
            bcount -= 2;
        }

        if ((meta_id & ID_UNIQUE) == desired_id) {
            if ((bcount - meta_bc) >= 0) {
                if (size)
                    *size = meta_bc - ((meta_id & ID_ODD_SIZE) ? 1 : 0);

                return dp;
            }
            else
                return NULL;
        }

        bcount -= meta_bc;
        dp += meta_bc;
    }

    return NULL;
}
