How to overcome the error cursor "" is not positioned on a row?

Question

PostgreSQL

I create a cursor

OPEN curs1 FOR SELECT * FROM leads_client WHERE status = 0;
UPDATE leads_client SET status = 1 WHERE CURRENT OF curs1;

And I try to update it, as a result I get an error
: Kernel error: ERROR: cursor "" is not positioned on a row;

Moreover, if you comment out the update line and get the data, then the lines in the cursor are:

loop
        fetch curs1 into r;
        if(r.id is nOT NULL) THEN 
            id := r.id;
            return next;
        END IF;
        if not(found) then exit; end if;
    end loop;