Summary:
When running with the packager in the tvOS simulator, reloading from the packager hits an assert in `RCTEventEmitter`, causing a crash. The solution is for `RCTTVNavigationEventEmitter` to check for the existence of the bridge before attempting to send an event.
Manual testing.
[IOS] [BUGFIX] [RCTTVNavigationEventEmitter.m] - Fix crash when reloading in tvOS
Closes https://github.com/facebook/react-native/pull/17797
Differential Revision: D7014975
Pulled By: hramos
fbshipit-source-id: 0bf766e87267ca8592ff0cc0b3cb4621a8e8f9b5