[Bug]: after removing last node new nodes not shown (they added but not shown)

### Describe the bug / 问题描述

In my project i delete nodes like this (picture below). After deleting i call render function so that everything is displayed correctly. as soon as i delete last node and then try to add new node, i don't see it on canvas. In fact it is added and it is transparent. If transparent node is moved, it will become visible. I also tried to use function for updating zindex after adding new node from this issue: https://github.com/antvis/G6/issues/6649, but it doesn't work for all my nodes. Is there any other and more correct solution?

### Reproduction link / 复现链接

_No response_

### Steps to Reproduce the Bug or Issue / 重现步骤

_No response_

### Version / 版本

Please select / 请选择

### OS / 操作系统

- [ ] macOS
- [x] Windows
- [ ] Linux
- [ ] Others / 其他

### Browser / 浏览器

- [x] Chrome
- [ ] Edge
- [ ] Firefox
- [ ] Safari (Limited support / 有限支持)
- [ ] IE (Nonsupport / 不支持)
- [ ] Others / 其他

The issue names no files or tests and provides no reproduction link, steps, version, or code. Start by reproducing the delete-last-node, render, and add-node sequence in the G6 canvas, then compare the suggested z-index update from issue 6649. Done means newly added nodes remain visible without being moved.

Written by the indexing model from the issue text.