[jdk21u-dev] RFR: 8350623: Fix -Wzero-as-null-pointer-constant warnings in nsk native test utilities

[Goetz Lindenmaier]

I backport this for parity with 21.0.10-oracle.

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Commit messages:
 - Backport 67dfdfa6ea829fcd1ecac0df8211b591ad15f859

Changes: https://git.openjdk.org/jdk21u-dev/pull/2394/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2394&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350623
  Stats: 7 lines in 2 files changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2394.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2394/head:pull/2394

PR: https://git.openjdk.org/jdk21u-dev/pull/2394