Add tests for the host checking logic, clarify the behaviors (#20328)

Before, the combination of AllowedDomains/BlockedDomains/AllowLocalNetworks is confusing.

This PR adds tests for the logic, clarify the behaviors.

modules/hostmatcher/hostmatcher.go

@@ -125,14 +125,14 @@ func (hl *HostMatchList) checkIP(ip net.IP) bool {
 
 // MatchHostName checks if the host matches an allow/deny(block) list
 func (hl *HostMatchList) MatchHostName(host string) bool {
+	if hl == nil {
+		return false
+	}
+
 	hostname, _, err := net.SplitHostPort(host)
 	if err != nil {
 		hostname = host
 	}
-
-	if hl == nil {
-		return false
-	}
 	if hl.checkPattern(hostname) {
 		return true
 	}