[jdk17u-dev] RFR: 8231490: Ugly racy writes to ZipUtils.defaultBuf

[Aleksey Shipilev]

Clean backport to fix a minor data race.

Additional testing:
 - [x] Linux x86_64 fastdebug, `java/nio/zipfs`, `java/util/zip`, `java/util/jar`

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Commit messages:
 - Backport 905e3e88137d46f90de7034e9fc324e97af873a6

Changes: https://git.openjdk.org/jdk17u-dev/pull/891/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=891&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8231490
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/891.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/891/head:pull/891

PR: https://git.openjdk.org/jdk17u-dev/pull/891