RFR: 8373024: JFR: CPU throttle rate can't handle incorrect values

[Erik Gahlin]

Could I get a review of a PR that hardens the CPU throttle rate setting?

Testing: test/jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/28636/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28636&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373024
  Stats: 5 lines in 3 files changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/28636.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28636/head:pull/28636

PR: https://git.openjdk.org/jdk/pull/28636