Close #80 创建ssl upstream发生在KNI accept线程，event_add后又通过promise_set_ctx修改了callback para，此时tfe work thread调用了peek client hello，导致取出空的ctx。

platform/src/ssl_stream.cpp

@@ -715,8 +715,8 @@ static void ssl_async_peek_client_hello(struct future * future, evutil_socket_t
 	struct peek_client_hello_ctx * ctx = ALLOC(struct peek_client_hello_ctx, 1);
 	ctx->ev = event_new(evbase, fd, EV_READ, peek_client_hello_cb, p);
 	ctx->logger = logger;
-	event_add(ctx->ev, NULL);
 	promise_set_ctx(p, (void *) ctx, peek_client_hello_ctx_free_cb);
+	event_add(ctx->ev, NULL);
 	return;
 }