fix 什么值得买排行榜为空报错 (#1758)

close #1706

lib/routes/smzdm/ranking.js

@@ -14,7 +14,7 @@ module.exports = async (ctx) => {
     const data = response.data.data.list;
     const list1 = [];
     const list2 = [];
-    for (let i = 0; i < 6; i++) {
+    for (let i = 0; i < Math.min(6, data.length); i++) {
         list1.push(data[i][0]);
         list2.push(data[i][1]);
     }