Once an `FSReqCallback` instance is created, it is a GC root until
the underlying fs operation has completed, meaning that it cannot
be garbage collected.
This is a problem when the underlying operation never starts
because an exception is thrown before that happens, for example
as part of parameter validation.
Instead, move all potentially throwing code before the `FSReqCallback`
creation.
PR-URL: https://github.com/nodejs/node/pull/35487
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
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