RFR: 8350771: Fix -Wzero-as-null-pointer-constant warning in nsk/monitoring ThreadController utilitiy

[David Holmes]

On Wed, 26 Feb 2025 12:23:16 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this trivial change to remove a use of literal zero as a null
> pointer constant in an nsk test utility.
> 
> 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 and trivial. Thanks

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23800#pullrequestreview-2655887064