🐞 Remove incorrect -delegates warning

fixes, when server is started with `-delegates` unset:

```
-delegates: arguments should be in the format "delegatedDomain=nameserver", not ""
```

integration_flags_test.go

@@ -173,7 +173,7 @@ var _ = Describe("flags", func() {
 				flags = []string{"-delegates="}
 			})
 			It("should give an informative message", func() {
-				Expect(string(serverSession.Err.Contents())).Should(MatchRegexp(`-delegates: arguments should be in the format "delegatedDomain=nameserver", not ""`))
+				Expect(string(serverSession.Err.Contents())).Should(Not(MatchRegexp(`-delegates`)))
 			})
 		})
 		When("the arguments are mangled", func() {

xip/xip.go

@@ -250,6 +250,9 @@ func NewXip(blocklistURL string, nameservers []string, addresses []string, deleg
 	}
 	// Parse and set the nameservers of our delegated domains
 	for _, delegate := range delegates {
+		if delegate == "" { // most common case: no delegates defined
+			continue
+		}
 		delegatedDomainAndNameserver := strings.Split(strings.ToLower(delegate), "=")
 		if len(delegatedDomainAndNameserver) != 2 {
 			logmessages = append(logmessages, fmt.Sprintf(`-delegates: arguments should be in the format "delegatedDomain=nameserver", not "%s"`, delegate))