fix: nas帮助中心union子句因无limit情况排序错误问题

app/mobile/controller/TopsNas.php

@@ -294,7 +294,7 @@ class TopsNas extends BaseController
         $model = \think\Db::table($sub_query . ' a');
         foreach ($categorys as $key => $val) {
             if ($key == 0) continue;
-            $model->union(function($query) use($val, $limit) {
+            $model->union(function($query) use($key, $val, $limit) {
                 $query->name('article')->field([
                     'id',
                     'cid',
@@ -308,6 +308,8 @@ class TopsNas extends BaseController
                 if (!empty($limit)) {
                     $query->limit($limit);
                 }
+                // 嵌套子查询，解决union没有limit时排序问题
+                $query->table($query->buildSql() . 'a' . $key);
             });
         }