react: example solution adds dependency incorrectly if given valid then invalid dependency ID

[petertseng]

https://github.com/exercism/xrust/pull/191/files#r78686049

[petertseng]

I know, it's just an example and isn't shown to students, and it still passes the tests anyway (it'd be quite difficult to write a test for this at all), but I don't like to set a bad example.