修正流式发送数据时，客户端异常断开后引起的段错误

platform/include/internal/platform.h

@@ -44,9 +44,6 @@ struct tfe_conn_private
 	evutil_socket_t fd;
 	struct bufferevent * bev;
 	uint8_t on_writing;
-	uint8_t closed;
-	uint8_t need_shutdown;
-	struct tfe_stream_write_ctx w_ctx;
 };
 
 struct tfe_stream_private
@@ -59,6 +56,8 @@ struct tfe_stream_private
 	struct tfe_thread_ctx * thread_ref;
 
 	enum tfe_stream_proto session_type;
+	struct tfe_stream_write_ctx * w_ctx_upstream;
+	struct tfe_stream_write_ctx * w_ctx_downstream;
 	struct tfe_conn_private * conn_upstream;
 	struct tfe_conn_private * conn_downstream;