Do not crash when event is emitted when ReactInstance is reloaded

Summary:
Regression introduced in D71735505 where I tried to ensure fabricEventEmitter was always non-null. Instead log a soft error when this happens, so we don't drop the event silently.

Changelog: [Android][Fixed] Fixed crash when event is emitted after instance is shutdown

Reviewed By: mdvacca

Differential Revision: D71967092

fbshipit-source-id: 990b6414b41a2709d70a6deae38f5aa043203a20