uev_timer_init(): Mark fd as uninitialized on error

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/timer.c

@@ -83,6 +83,7 @@ int uev_timer_init(uev_ctx_t *ctx, uev_t *w, uev_cb_t *cb, void *arg, int timeou
 		_uev_watcher_stop(w);
 	exit:
 		close(fd);
+		w->fd = -1;
 		return -1;
 	}