SSR broken when Navigator object is defined. Node JS 21.

Some environments have Navigator as an empty object even on the server.

Node JS v21 has navigator defined as an empty object.

This causes libraries like `echarts` to be incompatible with ssr and crash.

The problem is line `35` in `zrender/lib/core/env.js`

```ts
else if (typeof navigator === 'undefined')
```

Should ideally be:
```ts
else if (typeof window === 'undefined')
```