[C# client] `ScriptRPCEvent.WillAnswer` does not work

I'm using `WillAnswer` in my client RPC event handler but the server somehow gets `Answer not handled` error.

```csharp
Alt.OnScriptRPC += async (scriptRpcEvent, name, args, answerId) => {
    scriptRpcEvent.WillAnswer();
    await Task.Delay(1);
    await AltAsync.Do(() => {
        scriptRpcEvent.Answer("OK");
    });
};
```