anotehr fix for Item_func_isnotnull::not_null_tables()

mysql-test/r/join_outer.result:
  anotehr test for Item_func_isnotnull::not_null_tables()
mysql-test/t/join_outer.test:
  anotehr test for Item_func_isnotnull::not_null_tables()

mysql-test/r/join_outer.result

@@ -653,6 +653,10 @@ i	i	i
 select * from t1 natural left join t2 where (t2.i is not null)=0;
 i	i
 1	NULL
+select * from t1 natural left join t2 where (t2.i is not null) is not null;
+i	i
+1	NULL
+2	2
 drop table t1,t2,t3;
 create table t1 (f1 integer,f2 integer,f3 integer);
 create table t2 (f2 integer,f4 integer);

mysql-test/t/join_outer.test

@@ -431,6 +431,7 @@ insert into t2 values(2),(3);
 insert into t3 values(2),(4);
 select * from t1 natural left join t2 natural left join t3;
 select * from t1 natural left join t2 where (t2.i is not null)=0;
+select * from t1 natural left join t2 where (t2.i is not null) is not null;
 drop table t1,t2,t3;
 
 #

sql/item_cmpfunc.h

@@ -916,7 +916,8 @@ class Item_func_isnotnull :public Item_bool_func
   }
   const char *func_name() const { return "isnotnull"; }
   optimize_type select_optimize() const { return OPTIMIZE_NULL; }
-  table_map not_null_tables() const { return abort_on_null ? used_tables() : 0; }
+  table_map not_null_tables() const
+  { return abort_on_null ? not_null_tables_cache : 0; }
   Item *neg_transformer(THD *thd);
   void print(String *str);
   CHARSET_INFO *compare_collation() { return args[0]->collation.collation; }