PHJ file leak.

Hello. While looking a patch, I found that PHJ sometimes complains for
file leaks if accompanied by LIMIT.

Repro is very simple:

create table t as (select a, a as b from generate_series(0, 999999) a);
analyze t;
select t.a from t join t t2 on (t.a = t2.a) limit 1;

Once in several (or dozen of) times execution of the last query
complains as follows.

WARNING: temporary file leak: File 15 still referenced
WARNING: temporary file leak: File 17 still referenced

This is using PHJ and the leaked file was a shared tuplestore for
outer tuples, which was opend by sts_parallel_scan_next() called from
ExecParallelHashJoinOuterGetTuple(). It seems to me that
ExecHashTableDestroy is forgeting to release shared tuplestore
accessors. Please find the attached.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center