fix: add error checking in acl and poll

If aclPolicy is not defined, in updateAclPolicy, return an error.

poll.go

@@ -95,15 +95,16 @@ func (h *Headscale) PollNetMapHandler(ctx *gin.Context) {
 	now := time.Now().UTC()
 
 	// update ACLRules with peer informations (to update server tags if necessary)
-	err = h.UpdateACLRules()
-	if err != nil {
-		log.Error().
-			Caller().
-			Str("func", "handleAuthKey").
-			Str("machine", machine.Name).
-			Err(err)
+	if h.aclPolicy != nil {
+		err = h.UpdateACLRules()
+		if err != nil {
+			log.Error().
+				Caller().
+				Str("func", "handleAuthKey").
+				Str("machine", machine.Name).
+				Err(err)
+		}
 	}
-
 	// From Tailscale client:
 	//
 	// ReadOnly is whether the client just wants to fetch the MapResponse,