[jdk21u-dev] RFR: 8332717: ZGC: Division by zero in heuristics

[Liang Mao]

Clean backport of fixing division by zero in ZGC heuristics.

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Commit messages:
 - Backport 2d4185f4f1def7c32d1a556521e26ec656234220

Changes: https://git.openjdk.org/jdk21u-dev/pull/858/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=858&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332717
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/858.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/858/head:pull/858

PR: https://git.openjdk.org/jdk21u-dev/pull/858