Handle exception of network errors

[bechir]

When I'm not connected to internet and I try to test my code with PHPUnit, I got this error:

Invalid argument supplied for foreach() ... cleantalk/php-antispam/lib/Cleantalk.php:450

php-antispam/lib/Cleantalk.php

Lines 448 to 453 in 2515e28

	$servers = $this->get_servers_ip($url_host);
	// Loop until find work server
	foreach ($servers as $server) {

php-antispam/lib/Cleantalk.php

Lines 488 to 495 in 2515e28

	*/
	private function get_servers_ip($host)
	{
	if (!isset($host))
	return null;
	$servers = array();

The error is not handle, so this PR fix that issue

[Glomberg]

Approved