Make built-in DNS return NXDOMAIN for hosts mapped to empty array

[S-Tsunemori]

Since 4.37.3 it is possible to do this:

	"dns": {
		"hosts": {
			"dns.google": [
				"8.8.8.8",
				"8.8.4.4"
			]
		}
	}

I want to suggest to add a feature that return NXDOMAIN when an empty array [] is given.

---

I've noticed there're some strange random dns queries in my log, with some internet search I've found that the problem is caused by a feature that can't be turned off in Google Chrome browser. Detail: https://unix.stackexchange.com/questions/363512/chrome-dns-requests-with-random-dns-names-malware

So I tried to intercept those queries locally with v2ray so it doesn't have to go to remote server, this is my current setup:

	"dns": {
		"hosts": {
			"regexp:^[a-z]{7,15}$": "0.0.0.0",
			"regexp:^[a-z]{7,15}\\.lan$": "0.0.0.0"
		}
	}

For some reason there's a .lan suffix on desktop browser while no such suffix on mobile (Android). This workaround works but it returns 0.0.0.0 instead of standard behavior that returns NXDOMAIN.