Integrated: 8321939: [GenShen] ShenandoahOldEvacRatioPercent=100 fails with divide-by-zero

[William Kemper]

8321939: [GenShen] ShenandoahOldEvacRatioPercent=100 fails with divide-by-zero

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Commit messages:
 - Backport 2c77c16ef32d95f59a631e4a51836f4d6ccf4d39

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/6/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=6&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321939
  Stats: 173 lines in 3 files changed: 62 ins; 68 del; 43 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/6.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/6/head:pull/6

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/6