[jdk21u-dev] RFR: 8331863: DUIterator_Fast used before it is constructed

[Martin Doerr]

Clean backport of [JDK-8331863](https://bugs.openjdk.org/browse/JDK-8331863).

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Commit messages:
 - Backport 466a21d8646c05d91f29d607c6347afd34c75629

Changes: https://git.openjdk.org/jdk21u-dev/pull/703/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=703&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331863
  Stats: 2 lines in 1 file changed: 1 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/703.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/703/head:pull/703

PR: https://git.openjdk.org/jdk21u-dev/pull/703