Bug Hunt: empty object() + pattern() + unknown(false) fails to error

I wanted to validate an object that is used as a 'map' with keys of a specific format. So I used this pattern but it doesn't error:

````js
Joi.object().pattern(/\d/, Joi.number()).unknown(false)
````

Note I'm not sure about the expected error message but the test a never reaches that as we get an `AssertionError: expected null to exists` from the line above.