RFR: 8259383: AsyncGetCallTrace() crashes sporadically

[Lutz Schmidt]

Hi,
may I please ask the community to review this small fix? It closes another hole in AsyncGetCallTrace(). 
Thanks a lot!
Lutz

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Commit messages:
 - 8259383: AsyncGetCallTrace() crashes sporadically

Changes: https://git.openjdk.java.net/jdk/pull/2032/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2032&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259383
  Stats: 27 lines in 1 file changed: 22 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2032.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2032/head:pull/2032

PR: https://git.openjdk.java.net/jdk/pull/2032