Delete questionable loop at the beginning of csv_close()

[elfring]

I noticed the following loop in the implementation of the function “csv_close”.

    for (i = 0; i < MAXFLD; i++) {
        j = ctl->fld_index[ctl->fld_active[i]];
        if (j < 0)
            continue;
    }

💭 I find such a control flow not useful. Thus I suggest to remove it.