Hash join explain is broken

Hi!

After 5f32b29c explain of Hash Join sometimes triggers an error.

Simple reproduction case is below.

# create table t (x int);
CREATE TABLE
# set enable_sort = off;
SET
# explain select * from t a, t b where a.x = (select 1 where b.x = 1);
ERROR:  bogus varno: 65000

Before 5f32b29c the same case works OK.

# explain select * from t a, t b where a.x = (select 1 where b.x = 1);
                            QUERY PLAN
-------------------------------------------------------------------
 Hash Join  (cost=67.38..5311.24 rows=32512 width=8)
   Hash Cond: (a.x = (SubPlan 1))
   ->  Seq Scan on t a  (cost=0.00..35.50 rows=2550 width=4)
   ->  Hash  (cost=35.50..35.50 rows=2550 width=4)
         ->  Seq Scan on t b  (cost=0.00..35.50 rows=2550 width=4)
   SubPlan 1
     ->  Result  (cost=0.00..0.01 rows=1 width=4)
           One-Time Filter: (b.x = 1)
(8 rows)

Originally spotted by Nikita Glukhov.  I didn't investigate this case
further yet.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company