[jdk25u] RFR: 8370242: JFR: Clear event reference eagerly when using EventStream

[Erik Gahlin]

Could I have review of a clean backport? 

Thanks
Erik

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Commit messages:
 - Backport 65b32394187988abab99a8017eda39b1bd4a1782

Changes: https://git.openjdk.org/jdk25u/pull/372/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=372&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370242
  Stats: 11 lines in 2 files changed: 10 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk25u/pull/372.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/372/head:pull/372

PR: https://git.openjdk.org/jdk25u/pull/372