Fix NPE in FileReaderModule (#45287)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/45287

Fixes https://github.com/facebook/react-native/issues/45277

This fixes an NPE reported in OSS if you do this call in JavaScript:

```
 const fr = new FileReader();
 fr.readAsText({});
```

Changelog:
[Android] [Fixed] - Fix NPE in FileReaderModule

Reviewed By: dmytrorykun

Differential Revision: D59372620

fbshipit-source-id: ad5073376eaa26852c8277bdbb7d76b1aa480b3c