UNION ALL might return error when the first child is table dual

[winoros]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a int, b int);
set @@tidb_max_chunk_size=32;
select a from (select 100 as a, 100 as b union all select * from t) t where b != 0;

make sure that the number of satisfied rows from t is more than 32.

2. What did you expect to see? (Required)

Return the correct result.

3. What did you see instead (Required)

Error thrown Internal error: UnionExec chunk column count mismatch, req: 2, result: 1

4. What is your TiDB version? (Required)

[kennedy8312]

/type regression

[kennedy8312]

Regression Analysis
PR caused this regression: 35669