Minimum hugeint overflows in conversion to PG numeric

### Description

This query returns `0`:
```
select * from duckdb.query($$ select '-170141183460469231731687303715884105728'::hugeint as result $$);
```
But one higher works fine:

```
select * from duckdb.query($$ select '-170141183460469231731687303715884105728'::hugeint + 1 as result $$);
```

The reason for this is that [this line overflows](https://github.com/duckdb/pg_duckdb/blob/02ebeaec1b42619fab806fc881e67de0821b380d/src/pgduckdb_types.cpp#L274), because the positive 170141183460469231731687303715884105728 cannot be represented in a signed int128.

Found by #577