[Statepoint] Return undef value for the statepoint of the none token (#72552)

Helps avoid the crash in verifier when it tries to print the error.
`none` token might be produced by llvm-reduce, since it's a default
value, so by extension this also fixes llvm-reduce crash, allowing it to
just discard invalid IR.

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Co-authored-by: arpilipe <apilipenko@azul.com>