fix(plugin): prevent panic when ListenHosts is empty (#7565)

test/bind_test.go

@@ -0,0 +1,24 @@
+package test
+
+import "testing"
+
+func TestBind_FilterAll(t *testing.T) {
+	t.Parallel()
+	corefile := `.:0 {
+        bind 127.0.0.1 {
+            except 127.0.0.1
+        }
+        trace
+        loop
+        whoami
+    }`
+	inst, err := CoreDNSServer(corefile)
+	if inst != nil {
+		CoreDNSServerStop(inst)
+	}
+	if err == nil {
+		t.Log("server started; stopping immediately")
+	} else {
+		t.Logf("server failed to start as expected without listeners: %v", err)
+	}
+}