fix(channel): 修复渠道商品规则更新逻辑

- 添加对空规则的处理，避免保存空值- 优化 gid_rule、rule 和 order_limit_rule 的处理逻辑
- 提高代码可读性和稳定性

app/channel/controller/ChannelProduct.php

@@ -343,10 +343,13 @@ class ChannelProduct extends Controller
                         $gid_rule[$v] = $input;
                     }
                 }
+
                 if ($gid_rule) {
                     $gid_rule = json_encode($gid_rule);
                 }
 
+
+
                 $order_limit_rule = array();
                 foreach ($this->cash as $k => $v) {
                     $input = input('cash_order_limit_' . $k);
@@ -371,9 +374,13 @@ class ChannelProduct extends Controller
             $update['percent_type'] = $percent_type;
             if ($rule) {
                 $update['rule'] = $rule;
+            }else{
+                $update['rule'] = null;
             }
             if ($gid_rule) {
                 $update['gid_rule'] = $gid_rule;
+            }else{
+                $update['gid_rule'] = null;
             }
             $gid = input('gid');
             if ($gid) {
@@ -382,6 +389,8 @@ class ChannelProduct extends Controller
 
             if ($order_limit_rule) {
                 $update['order_limit_rule'] = $order_limit_rule;
+            }else{
+                $update['order_limit_rule'] = null;
             }
             $order_limit = input('order_limit');
             $update['order_limit'] = $order_limit;