Protobuf Output Converts "" and 0 to NULL for Nullable columns

### Company or project name

ClickHouse/pg_chdb

### Describe what's wrong

Empty string and zero values from Nullable columns return as NULL rather than an empty string or 0.

### Does it reproduce on the most recent release?

Yes

### How to reproduce

```
ClickHouse client version 26.7.2.11 (official build).
Connecting to localhost:9000 as user default.
Connected to ClickHouse server version 26.7.2.

Mac :) INSERT INTO FUNCTION file('test.tmp', 'Protobuf', 'a Nullable(Int64), b String, c Nullable(String)')
VALUES (0, '', '')
Ok.

Mac :) SELECT * FROM file('test.tmp', 'Protobuf', 'a Nullable(Int64), b String, c Nullable(String)')
┌────a─┬─b─┬─c────┐
1. │ ᴺᵁᴸᴸ │ │ ᴺᵁᴸᴸ │
└──────┴───┴──────┘
```

### Expected behavior

```
Mac :) SELECT * FROM file('test.tmp', 'Protobuf', 'a Nullable(Int64), b String, c Nullable(String)')
┌─a─┬─b─┬─c─┐
1. │ 0 │ │ │
└───┴───┴───┘
```

### Error message and/or stacktrace

_No response_

### Related issues and pull requests

chdb-io/chdb-core#152

### Additional context

_No response_