And recreate it if it does not exist.
In windows, electron renderer process will crash if:
1. Import some NAPI module that enable `tokio-rt` flag in renderer process.
2. Reload the page.
3. Call a function imported from that NAPI module.
Because the tokio runtime will be dropped when reloading the page, and won't create again, but currently we assume that the runtime must exist in tokio-based `within_runtime_if_available`.
This will cause some panic like this:
```
thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', napi-rs\crates\napi\src\tokio_runtime.rs:72:42
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Error: Renderer process crashed: crashed, exitCode: -529697949
at EventEmitter.<anonymous> (napi-rs\examples\napi\electron.js:33:9)
at EventEmitter.emit (node:events:525:35)
```
we need this to be able to safely drop an struct,
that makes use of an async task.
the drop function needs to be able to call `.abort()`
on the join handle to avoid memory corruption and undefined bahviour.
