uv-unix: set stream->accepted_fd=-1 in uv_pipe_init()

stream->accepted_fd was zeroed in uv_pipe_init() and that made
uv__finish_close() close the stdin file descriptor. Not good.

src/uv-unix.c

@@ -1838,6 +1838,7 @@ int uv_pipe_init(uv_pipe_t* handle) {
   ev_init(&handle->read_watcher, uv__stream_io);
   handle->write_watcher.data = handle;
   handle->read_watcher.data = handle;
+  handle->accepted_fd = -1;
   handle->fd = -1;
 
   ngx_queue_init(&handle->write_completed_queue);