aria2.open() did not validate secret.

aria2 secret: '123'

```ts
const aria2 = new Aria2RPC(
      host: 'localhost',
      port: 6800,
      secure: false,
      secret: '',  // No '123'
      path: '/jsonrpc'
);

aria2
    .open()
    .then(() => console.log('open'))
    .catch(() => console.log('error'))

// expect 'error'
// But 'open'
```