fix query param struct filling

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

handler.go

@@ -487,11 +487,13 @@ func (h *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
+	if len(matches) > 0 {
 		matches = rflutil.FlattenMap(matches)
 		if err = rflutil.Merge(argv.Interface(), matches, rflutil.SliceAppend(true), rflutil.Tags([]string{"protobuf", "json"})); err != nil {
 			h.errorHandler(ctx, handler, w, r, err, http.StatusBadRequest)
 			return
 		}
+	}
 
 	hr := &rpcRequest{
 		codec:       cf,