Fix for closing and re-opening non-fullscreen modals on iOS fast not working correctly

[Digifais]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

This is a new bug fix for #3546 since #4040 didn't completely fix this. When showing a non-fullscreen modal, swipe to close, re-open it fast, repeat if needed for x amount of times, the following error is thrown in the application output:

[Presentation] Attempt to present <MvvmCross_Platforms_Ios_Views_MvxNavigationController: 0x7fdae1b74a00> on <MvvmCross_Platforms_Ios_Views_MvxNavigationController: 0x7fdae69c8c00> (from <MvvmCross_Platforms_Ios_Views_MvxNavigationController: 0x7fdae69c8c00>) whose view is not in the window hierarchy.

⤵️ What is the current behavior?

Error from #3546 still sometimes occurs when closing and re-opening non-fullscreen modals on iOS fast.

🆕 What is the new behavior (if this is a feature change)?

Closing and re-opening non-fullscreen modals on iOS fast should work correctly now.

💥 Does this PR introduce a breaking change?

No

🐛 Recommendations for testing

Show a non-fullscreen modal, swipe to close, re-open it fast, repeat if needed for x amount of times.

📝 Links to relevant issues/docs

#3546
#4040

🤔 Checklist before submitting

• All projects build
• Follows style guide lines (code style guide)
• Relevant documentation was updated (docs style guide)
• Rebased onto current develop

[Cheesebaron]

Thank you for the PR 😃