fixed edge cases when web service returns unexpected name and address format

on validating VAT number ES00159660V, here is the raw output from the webservice:

```
stdClass Object
(
    [countryCode] => ES
    [vatNumber] => 00159660V
    [requestDate] => 2014-05-29+02:00
    [valid] => 1
    [name] => ---
    [address] => ---
)
```

We can see that this VAT number is valid, but the name and address format are unexpected by the check function, resulting in the following PHP notices:

```
Notice: Undefined offset: 1 in /Users/yann/www-dev/vat-validation/src/Snowcap/Vat/Validation.php on line 70
Notice: Undefined offset: 1 in /Users/yann/www-dev/vat-validation/src/Snowcap/Vat/Validation.php on line 71
Notice: Undefined offset: 1 in /Users/yann/www-dev/vat-validation/src/Snowcap/Vat/Validation.php on line 81
```

I added checks before assigning $denomination, $name, $streetline, $cityline, $zip and $city vars.