[5.3] Catch dns_get_record possible warnings in validateActiveUrl

[litvinchuk]

In some cases dns_get_record can throw warnings

• An unexpected server failure occurred.
• A temporary server error occurred.
• DNS Query failed

[cyrossignol]

@litvinchuk @taylorotwell @GrahamCampbell Thanks for the change. Unfortunately, this PR doesn't fix a certain scenario:

If the IPv6 stack isn't configured properly somewhere between the server and the internet, PHP warns, dns_get_record(): Unable to parse DNS data received on line 1, probably because we're attempting to fetch AAAA records as well as A.

As a result, validation fails for valid IPv4 lookups as well.

Arguably, we could suggest that users get their IPv6 working correctly, but this seems unreasonable, especially for applications deployed on an IPv4 intranet. Docker users will likely encounter confusion as well because containers disable IPv6 by default, and nothing in the docs or error hint at this limitation. This may also be the reason why we see some homestead users having problems with active_url validation.

I'm not sure if this warrants a separate issue ticket. Perhaps we can separate the validation checks for IPv4 and IPv6:

if ($url = parse_url($value, PHP_URL_HOST)) {
    try {
        if (count(dns_get_record($url, DNS_A)) > 0) {
            return true;
        }
    } catch (Exception $e) {
    }

    try {
        if (count(dns_get_record($url, DNS_AAAA)) > 0)
            return true;
        }
    } catch (Exception $e) {
    }

    return false;
}

The extra lookup is expensive, but adds flexibility.