Declarating a duplicated error name in a .sdkgen file will produce a invalid node-server code

When is declared a duplicate error types in skdgen no advice or error are presented by the compiler and this will produce a invalid typescript code.

iex.
```

error NotLoggedIn
error WrongLogin
error InvalidCall
error InvalidToken

error NotLoggedIn
error WrongLogin
error InvalidCall
error InvalidToken
```
