Summary:
This is a critical change and should be pushed to stabel asap
The reason for the pull request is to prevent crashes that can occure if the function relativeKeyboardHeight(keyboardFrame: ScreenRect) got null as an input variable which sometimes does happen.
Closes https://github.com/facebook/react-native/pull/10287
Differential Revision: D3988359
Pulled By: bestander
fbshipit-source-id: 0d1052b590b2684907ea6f7d6b4fe9b89989d4dd