RFR: 8346052: JFR: Incorrect average value in 'jfr view'

[Erik Gahlin]

Could I have a review of PR that fixes an issue with 'jfr view' when calculating the average for a timespan.

Testing: jdk/jdk/rf

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/22699/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22699&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346052
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/22699.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22699/head:pull/22699

PR: https://git.openjdk.org/jdk/pull/22699