Small bug fix

src/core/mainloop/connection.c

@@ -4572,7 +4572,7 @@ connection_write_to_buf_impl_,(const char *string, size_t len,
     struct buf_t *outbuf = conn->safe_conn->outbuf;
 
     if (zlib) {
-      size_t old_datalen = buf_datalen(conn->outbuf);
+      size_t old_datalen = buf_datalen(outbuf);
       dir_connection_t *dir_conn = TO_DIR_CONN(conn);
       int done = zlib < 0;
       CONN_LOG_PROTECT(conn, r = buf_add_compress(outbuf,