avoid flushes for buffering

src/vdp_pesi.c

@@ -2017,6 +2017,7 @@ pesi_buf_bytes(struct req *req, enum vdp_action act, void **priv,
 			return (tree->retval);
 		}
 		else {
+			node->data.act = VDP_NULL;
 			AZ(node->data.st->len);
 			assert(node->data.st->space == len);
 			memcpy(node->data.st->ptr, ptr, len);