RFR: 8335592: Fix -Wzero-as-null-pointer-constant warnings in RootNode ctor

[Kim Barrett]

On Wed, 3 Jul 2024 05:30:25 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> Please review this trivial change to the RootNode constructor. Both arguments
>> to the LoopNode base class constructor are changed from 0 to nullptr. This
>> removes some -Wzero-as-null-pointer-constant warnings when building with that
>> enabled.
>> 
>> Testing: mach5 tier1
>
> Looks good and trivial.

Thanks for review @TobiHartmann

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PR Comment: https://git.openjdk.org/jdk/pull/19997#issuecomment-2205155609