RFR: 8375737: Fix -Wzero-as-null-pointer-constant warnings in arm32 code

[David Holmes]

On Tue, 20 Jan 2026 18:27:26 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this trivial change to arm32 code to avoid using literal zero as a null
> pointer constant, instead using nullptr.
> 
> Testing: GHA build for arm32

Good and trivial. Thanks

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/29328#pullrequestreview-3685373003