Fix crash inside RCTRedBox when trying to present same UIViewController twice
Fix crash inside RCTRedBox when trying to present same UIViewController twice

Summary:
Calling `-[RCTRedBox showErrorMessage]` twice causes a crash

We used `-[UIViewController isBeingPresented]` to tell whether view controller is already presented.
But from the documentation:

> A Boolean value indicating whether the view controller is being presented.

Source: https://developer.apple.com/documentation/uikit/uiviewcontroller/2097564-beingpresented?language=objc#

 ---
So this means that if you present it, wait until presentation animation is finished and then call `-[RCTRedBox showErrorMessage]` again, following exception will be thrown.

```
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Application tried to present modally an active controller <UIViewController: 0x7fc33e422f50>.'
```

Changelog: Fix crash caused by presenting view controller twice from RCTRedBox

Reviewed By: PeteTheHeat

Differential Revision: D20946645

fbshipit-source-id: 763066e37db4e56efb0118b2e7867ad0724bae81

facebook/react-native,facebook/react-native,facebook/react-native,arthuralee/react-native,myntra/react-native,hammerandchisel/react-native,pandiaraj44/react-native,janicduplessis/react-native,arthuralee/react-native,javache/react-native,arthuralee/react-native,myntra/react-native,javache/react-native,hoangpham95/react-native,hoangpham95/react-native,janicduplessis/react-native,facebook/react-native,hammerandchisel/react-native,facebook/react-native,hoangpham95/react-native,javache/react-native,hammerandchisel/react-native,javache/react-native,arthuralee/react-native,myntra/react-native,myntra/react-native,hammerandchisel/react-native,pandiaraj44/react-native,janicduplessis/react-native,myntra/react-native,pandiaraj44/react-native,facebook/react-native,janicduplessis/react-native,janicduplessis/react-native,javache/react-native,hoangpham95/react-native,facebook/react-native,janicduplessis/react-native,myntra/react-native,hammerandchisel/react-native,javache/react-native,myntra/react-native,javache/react-native,pandiaraj44/react-native,facebook/react-native,hoangpham95/react-native,facebook/react-native,hammerandchisel/react-native,javache/react-native,pandiaraj44/react-native,pandiaraj44/react-native,arthuralee/react-native,myntra/react-native,hoangpham95/react-native,hoangpham95/react-native,hammerandchisel/react-native,myntra/react-native,pandiaraj44/react-native,hoangpham95/react-native,janicduplessis/react-native,hammerandchisel/react-native,pandiaraj44/react-native,javache/react-native,janicduplessis/react-native