Fix ios multiple flutter presenting error

[AlexT84]

Connection with issue(s)

Resolve issue #???
This resolves the issue on iOS with the flutter_inappwebview used in multiple flutters native app.

Connected to #???

Testing and Review Notes

To test the fix just create a flutterViewController, flutter engine, load a flutter project in to a native tabbar app and try to use flutter_inappwebview from the flutter code.
The result will be that nothing will be presented to the user and te console will output:
[Presentation] Attempt to present <flutter_inappwebview.SafariViewController: 0x7fb4470ad200> on <Koala.RootNavigationController: 0x7fb4b4982e00> (from <Koala.RootNavigationController: 0x7fb4b4982e00>) whose view is not in the window hierarchy.

Screenshots or Videos

To Do

• double check the original issue to confirm it is fully satisfied
• add testing notes and screenshots in PR description to help guide reviewers
• request the "UX" team perform a design review (if/when applicable)

[pichillilorenzo]

@all-contributors please add @AlexT84 for code

[allcontributors]

@pichillilorenzo

I've put up a pull request to add @AlexT84! 🎉