fix(api): 修复 reply_to_platform_id 可能未定义的问题

src/plugin_system/apis/send_api.py

@@ -196,6 +196,7 @@ async def _send_to_target(
             )            
         else:
             anchor_message = None
+            reply_to_platform_id = None
 
         # 构建发送消息对象
         bot_message = MessageSending(