vertx-db2-client character encoding problem

### Version

3.9.4 and 4.0.0.Beta3

### Context

when query data with vertx-db2-client, non ascii characters(for example, chinese characters) not encoded correctly

### Steps to reproduce

```kotlin
...
val rs = pool.connection.await().query("select * from V_ITEMS").execute().await()
val list = Sequence(rs::iterator).map(Row::toJson).toList()
println(Json.encode(list))
...
```