RFR: 8282947 JFR: Dump on shutdown live-locks in some conditions

[Erik Gahlin]

Could I have review that fixes a livelock when using /dev/null as dump path.

Testing: test/jdk/jdk/jfr + tier1

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Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/8891/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8891&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282947
  Stats: 66 lines in 3 files changed: 62 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8891.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8891/head:pull/8891

PR: https://git.openjdk.java.net/jdk/pull/8891