RFR: 8345684: Prevent NPE in OperatingSystemImpl#isCpuSetSameAsHostCpuSet

[Fabian Meumertzheim]

The return value of Metrics#getCpuSetCpus may change over time, including from non-null to null across the two calls in this method.

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Commit messages:
 - 8345684: Prevent NPE in OperatingSystemImpl#isCpuSetSameAsHostCpuSet

Changes: https://git.openjdk.org/jdk/pull/22611/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22611&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345684
  Stats: 5 lines in 1 file changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/22611.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22611/head:pull/22611

PR: https://git.openjdk.org/jdk/pull/22611