Fix crash in RNTester when removing/developing tests (#23406)
Fix crash in RNTester when removing/developing tests (#23406)

Summary:
Ensure that the current openExample (stored in AsyncStorage) exists in the module list.

It's possible for the example to be missing if a test was removed & previously open in RNTester OR when actively developing RNTester tests & switching between branches

[General] [Fixed] - Potential crash in RNTester when removing/developing test cases
Pull Request resolved: https://github.com/facebook/react-native/pull/23406

Differential Revision: D14055695

Pulled By: cpojer

fbshipit-source-id: 6cf00e097e934f7a342e7d210b6319e1cba142ca

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