Failing test case
Maintain other error messages when setting default

Fixes the case for when `numericality` doesn't have a message, but other options do:

```js
validations: {
  integer_attribute: {
    numericality: {
      onlyInteger: true,
      messages: {
        onlyInteger: 'Distancia entre surcos debe ser un número'
      }
    }
  }
}
```