RFR: 8350767: Fix -Wzero-as-null-pointer-constant warnings in nsk jni stress tests

[Coleen Phillimore]

On Wed, 26 Feb 2025 12:10:38 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to remove uses of literal zero as a null pointer
> constant in nsk jni stress tests.
> 
> Testing: mach5 tier1
> Locally tested (linux-x64) with -Wzero-as-null-pointer-constant enabled to
> verify the warnings associated with this code were removed.

Looks good (I don't believe test changes like these require 24 hour review perioid).  Also it's a trivial change.

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Marked as reviewed by coleenp (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23798#pullrequestreview-2654389578