Summary:Fix for issue #6300:
Motivation: When more than one callback is registered to a native module, the error message that a user receives is not indicative of what is really happening.
Closes https://github.com/facebook/react-native/pull/6436
Differential Revision: D3087551
Pulled By: tadeuzagallo
fb-gh-sync-id: 93c703348dc53b75c5b507edc71754680ab5c438
shipit-source-id: 93c703348dc53b75c5b507edc71754680ab5c438