- windows: install: fix crash due to empty DHCP server pointer

#2036

Squashed commit of the following:

commit 5c70d28b241d1a98e034f6798dade073b1b42511
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Mon Aug 24 18:42:21 2020 +0300

    - windows: install: fix crash due to empty DHCP server pointer

    We should not assign a Go interface value, otherwise `==nil` check doesn't work.

dnsforward/dnsforward.go

@@ -82,9 +82,9 @@ func NewServer(p DNSCreateParams) *Server {
 	s.dnsFilter = p.DNSFilter
 	s.stats = p.Stats
 	s.queryLog = p.QueryLog
-	s.dhcpServer = p.DHCPServer
 
-	if s.dhcpServer != nil {
+	if p.DHCPServer != nil {
+		s.dhcpServer = p.DHCPServer
 		s.dhcpServer.SetOnLeaseChanged(s.onDHCPLeaseChanged)
 		s.onDHCPLeaseChanged(dhcpd.LeaseChangedAdded)
 	}

home/dns.go

@@ -62,10 +62,12 @@ func initDNSServer() error {
 	Context.dnsFilter = dnsfilter.New(&filterConf, nil)
 
 	p := dnsforward.DNSCreateParams{
-		DNSFilter:  Context.dnsFilter,
-		Stats:      Context.stats,
-		QueryLog:   Context.queryLog,
-		DHCPServer: Context.dhcpServer,
+		DNSFilter: Context.dnsFilter,
+		Stats:     Context.stats,
+		QueryLog:  Context.queryLog,
+	}
+	if Context.dhcpServer != nil {
+		p.DHCPServer = Context.dhcpServer
 	}
 	Context.dnsServer = dnsforward.NewServer(p)
 	dnsConfig := generateServerConfig()