Summary:
When attempting to inverse a Bash boolean, the `!` character converts the meaning to become `[[ ! -n false ]]` (checking that the string "false" is empty) which never matches, and therefore this condition can never occur.
See https://stackoverflow.com/a/2953673
Closes https://github.com/facebook/react-native/pull/14190
Differential Revision: D5137013
Pulled By: javache
fbshipit-source-id: 7df52cc90a4ab79c7b5da54dbfb6c99fba3e8b80
