RFR: 8318019: GenShen: Fix assertion to allow empty evacuation cycles

[Kelvin Nilsen]

On Wed, 11 Oct 2023 16:27:18 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

> Assertion needs to allow for gc phase EVACUATION even if no forwarding objects because we are only promoting in place.

After testing, I'll match this to a JBS issue.

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PR Comment: https://git.openjdk.org/shenandoah/pull/337#issuecomment-1758066648