Bug#54494 crash with explain extended and prepared statements

In case of outer join and emtpy WHERE conditon
'always true' condition is created for WHERE clasue.
Later in mysql_select() original SELECT_LEX WHERE
condition is overwritten with created cond.
However SELECT_LEX condition is also used as inital
condition in mysql_select()->JOIN::prepare().
On second execution of PS modified SELECT_LEX condition
is taken and it leads to crash.
The fix is to restore original SELECT_LEX condition
(set to NULL if original cond is NULL) in
 reinit_stmt_before_use().
HAVING clause is fixed too for safety reason
(no test case as I did not manage to think out
 appropriate example).

mysql-test/r/ps.result

@@ -3001,4 +3001,24 @@ EXECUTE stmt;
 1
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1;
+#
+# Bug#54494 crash with explain extended and prepared statements
+#
+CREATE TABLE t1(a INT);
+INSERT INTO t1 VALUES (1),(2);
+PREPARE stmt FROM 'EXPLAIN EXTENDED SELECT 1 FROM t1 RIGHT JOIN t1 t2 ON 1';
+EXECUTE stmt;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	
+Warnings:
+Note	1003	select 1 AS `1` from `test`.`t1` `t2` left join `test`.`t1` on(1) where 1
+EXECUTE stmt;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	
+Warnings:
+Note	1003	select 1 AS `1` from `test`.`t1` `t2` left join `test`.`t1` on(1) where 1
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1;
 End of 5.1 tests.

mysql-test/t/ps.test

@@ -3079,4 +3079,15 @@ EXECUTE stmt;
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1;
 
+--echo #
+--echo # Bug#54494 crash with explain extended and prepared statements
+--echo #
+CREATE TABLE t1(a INT);
+INSERT INTO t1 VALUES (1),(2);
+PREPARE stmt FROM 'EXPLAIN EXTENDED SELECT 1 FROM t1 RIGHT JOIN t1 t2 ON 1';
+EXECUTE stmt;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1;
+
 --echo End of 5.1 tests.

sql/sql_prepare.cc

@@ -2362,11 +2362,15 @@ void reinit_stmt_before_use(THD *thd, LEX *lex)
         sl->where= sl->prep_where->copy_andor_structure(thd);
         sl->where->cleanup();
       }
+      else
+        sl->where= NULL;
       if (sl->prep_having)
       {
         sl->having= sl->prep_having->copy_andor_structure(thd);
         sl->having->cleanup();
       }
+      else
+        sl->having= NULL;
       DBUG_ASSERT(sl->join == 0);
       ORDER *order;
       /* Fix GROUP list */