[Bug] AO column table can't process zero-column table

### Apache Cloudberry version

main branch, with cassert

### What happened

```sql
set default_table_access_method = ao_column;
create table t1();
create index on t1 using btree ((1)); -- assert fail

insert into t1 default values;
select * from t1;

delete from t1;
select * from t1;

insert into t1 default values;
select * from t1;
```

The above query will crash.

### What you think should happen instead

The above query should has the same behavior as heap tables.

### How to reproduce

```sql
set default_table_access_method = ao_column;
create table t1();
create index on t1 using btree ((1)); -- assert fail

insert into t1 default values;
select * from t1;

delete from t1;
select * from t1;

insert into t1 default values;
select * from t1;
```

### Operating System

no spec

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes, I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/cloudberry/blob/main/CODE_OF_CONDUCT.md).

Start by running the provided SQL reproduction on the main branch with cassert enabled, then compare the ao_column results with heap tables. Trace the zero-column table, index creation, insert, and delete paths; done means the assertion no longer occurs and the queries behave like heap tables.

Written by the indexing model from the issue text.