method isAvailable() returns TRUE when extension doesn't exist

[IvoMiranda]

Example:
thisdomain.doesnotexistatall
$domain->isAvailable() returns TRUE

[NabiKAZ]

I fixed this bug.
After accept pull request you can try this:

<?php
require_once __DIR__.'/../vendor/autoload.php';

$sld = ' thisdomain.doesnotexistatall';

try {
    $domain = new Phois\Whois\Whois($sld);
} catch (InvalidArgumentException $e) {
    die($e->getMessage()."\n");
}

if ($domain->isAvailable()) {
    echo "Domain is available\n";
} else {
    echo "Domain is registered\n";
}

Output:

Domain name isn't valid!

Or you can get a fork from my repository: https://github.com/NabiKAZ/php-whois/