use assert1 func (#2783)

routergroup.go

@@ -214,9 +214,7 @@ func (group *RouterGroup) createStaticHandler(relativePath string, fs http.FileS
 
 func (group *RouterGroup) combineHandlers(handlers HandlersChain) HandlersChain {
 	finalSize := len(group.Handlers) + len(handlers)
-	if finalSize >= int(abortIndex) {
-		panic("too many handlers")
-	}
+	assert1(finalSize < int(abortIndex), "too many handlers")
 	mergedHandlers := make(HandlersChain, finalSize)
 	copy(mergedHandlers, group.Handlers)
 	copy(mergedHandlers[len(group.Handlers):], handlers)