[jdk17u-dev] RFR: 8270336: [TESTBUG] Fix initialization in NonbranchyTree

[Goetz Lindenmaier]

I backport this for parity with 17.0.4-oracle.

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Commit messages:
 - Backport 3cadc3606073f0efc2e97dda348ffb65c41dad0c

Changes: https://git.openjdk.java.net/jdk17u-dev/pull/218/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u-dev&pr=218&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270336
  Stats: 30 lines in 1 file changed: 4 ins; 17 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk17u-dev/pull/218.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u-dev pull/218/head:pull/218

PR: https://git.openjdk.java.net/jdk17u-dev/pull/218