RFR: JDK-8263559: Add missing initializers to VM_PopulateDumpSharedSpace [v2]

[Thomas Stuefe]

On Sun, 14 Mar 2021 23:17:27 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove explicit NULL resets
>
> Oops,  agree with Kim. The later assignments to NULL should be removed.

Kim, Ioi, thanks. I removed the explicit NULL assignments.

Side note, I know VM_op::do_it() is supposed to run only once, and in straight succession from constructing the object, but I wonder if it would make sense to assert this.

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PR: https://git.openjdk.java.net/jdk/pull/2996