[jdk11u-dev] RFR: 8287073: NPE from CgroupV2Subsystem.getInstance()

[Severin Gehwolf]

Backport fixing a potential NPE on cgroups v2.

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Commit messages:
 - Backport 744b822ab194a0f7ef4e7a4053be32c6a0889efc

Changes: https://git.openjdk.org/jdk11u-dev/pull/1339/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1339&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8287073
  Stats: 4 lines in 1 file changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1339.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1339/head:pull/1339

PR: https://git.openjdk.org/jdk11u-dev/pull/1339