Incorrect display of subquery cache in union.result

# 

# Bug #49734: Crash on EXPLAIN EXTENDED UNION ... ORDER BY 

#   <any non-const-function>

# 

CREATE TABLE t1 (a VARCHAR(10), FULLTEXT KEY a (a));

INSERT INTO t1 VALUES (1),(2);

CREATE TABLE t2 (b INT);

INSERT INTO t2 VALUES (1),(2);

EXPLAIN EXTENDED

SELECT * FROM t1 UNION SELECT * FROM t1

ORDER BY (SELECT a FROM t2 WHERE b = 12);

id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	

2	UNION	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	

NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL	NULL	Using filesort

3	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where

Warnings:

Note	1276	Field or reference 'a' of SELECT #3 was resolved in SELECT #-1

Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` union select `test`.`t1`.`a` AS `a` from `test`.`t1` order by <expr_cache><>((select `a` from `test`.`t2` where (`test`.`t2`.`b` = 12)))

<expr_cache><>((select `a` from `test`.`t2` where (`test`.`t2`.`b` = 12)))