And add a better error message.

By using `void` instead of `await`, any error thrown is not caught
by surrounding try-catch blocks.

I could continue to use `void` and explicitly handle any thrown errors
by using `.catch`, but most likely the time savings is minimal and
this makes the code more complex.

Discussion here #882 (comment)
shows that properly handling preloading feature flag errors is complex
and the benefit we get from it does not offset the complexity.