Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/45549
## Summary
Calling `getCurrentReactContext` on an unmounted `ReactRootView` could lead to a NPE. The method currently returns a nullable value so return type is the exact same. This change checks if the react instance manager is present and returns null early if not.
## Changelog:
[Android] [Fixed] - Adds a null check in react context getter
Reviewed By: zeyap
Differential Revision: D59982179
fbshipit-source-id: bac5c12e7dc4ee3296991063eb3746141b8446bc