RFR: 8345050: Fix -Wzero-as-null-pointer warning in MemPointer ctor

[Christian Hagedorn]

On Tue, 26 Nov 2024 11:00:56 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this trivial change to use nullptr instead of a literal 0 in a
> call to Node::dump_bfs by the MemPointer ctor.
> 
> Testing: mach5 tier1

Looks good and trivial.

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Marked as reviewed by chagedorn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22388#pullrequestreview-2461145711