SQLite Forum: Possible bug: Unexpected result using correlated aggregate subquery

The following examples demonstrate a possible bug in some cases when using a correlated aggregate subquery:

```sql
SQLite version 3.37.0 2021-08-30 17:02:48
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database.
sqlite> CREATE TABLE x AS SELECT 1 a;
sqlite> CREATE TABLE y AS SELECT 1 b UNION ALL SELECT 1;
sqlite>
sqlite> .mode box
sqlite>
sqlite> SELECT (SELECT group_concat(a) FROM y) unexpected, -- expected 1,1
   ...>        group_concat((SELECT a FROM y)) expected,
   ...>        (SELECT group_concat(b) FROM y) expected,
   ...>        (SELECT group_concat(a+b) FROM y) expected
   ...>   FROM x;
┌────────────┬──────────┬──────────┬──────────┐
│ unexpected │ expected │ expected │ expected │
├────────────┼──────────┼──────────┼──────────┤
│ 1          │ 1        │ 1,1      │ 2,2      │
└────────────┴──────────┴──────────┴──────────┘
sqlite>
sqlite> INSERT INTO x VALUES (1);
sqlite>
sqlite> SELECT (SELECT group_concat(a) FROM y) unexpected -- expected 2 rows
   ...>   FROM x;
┌────────────┐
│ unexpected │
├────────────┤
│ 1,1        │
└────────────┘
sqlite>
sqlite> SELECT (SELECT group_concat(b) FROM y) expected
   ...>   FROM x;
┌──────────┐
│ expected │
├──────────┤
│ 1,1      │
│ 1,1      │
└──────────┘
sqlite>
sqlite> SELECT (SELECT group_concat(a+b) FROM y) expected
   ...>   FROM x;
┌──────────┐
│ expected │
├──────────┤
│ 2,2      │
│ 2,2      │
└──────────┘
```