Only validate the signature with the content if the first non-content validation fails

PR Summary

When ExecutionPolicy is set to require a signature, under some circumstances a signature placed in a file will not execute with a "hash mismatch" error, even though Get-AuthenticodeSignature will return that the signature is valid.
This is because Get-AuthenticodeSignature and our invocation path are not symmetrical. This PR adds the same check that we do in Get-AuthenticodeSignature into our invocation path.

PR Context

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