Invoke-DownloadWithProgress runs Invoke-WebRequest in a separate runspace,
where an HTTP or DNS failure is non-terminating: EndInvoke returned normally,
the caller skipped the mirror, and Get-FileHash died on a file that was never
written. Rethrow the runspace's first error outside the unwrapping catch, so
the caller sees the same WebException/HttpResponseException it classifies.
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