feat(nameserver): correct impl of UpdateTopicRouteInfo (#406)

default Topic is extra for UpdateTopicRouteInfo, and will cause incorrect config to retry topic.

Closes #404
diff --git a/internal/route.go b/internal/route.go
index 181ebe9..d3a5f01 100644
--- a/internal/route.go
+++ b/internal/route.go
@@ -118,13 +118,10 @@
 
 	routeData, err := s.queryTopicRouteInfoFromServer(topic)
 	if err != nil {
-		routeData, err = s.queryTopicRouteInfoFromServer(defaultTopic)
-		if err != nil {
-			rlog.Warning("query topic route from server error", map[string]interface{}{
-				rlog.LogKeyUnderlayError: err,
-			})
-			return nil, false
-		}
+		rlog.Warning("query topic route from server error", map[string]interface{}{
+			rlog.LogKeyUnderlayError: err,
+		})
+		return nil, false
 	}
 
 	if routeData == nil {