RFR: Check that pointer is in heap before checking the affiliation of owning region [v2]

[Roman Kennke]

On Thu, 22 Jul 2021 17:46:51 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> This is a small bug fix that was meant to go in with the concurrent remembered set scanning changes
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert unrelated change to comment

Ok.

-------------

Marked as reviewed by rkennke (Lead).

PR: https://git.openjdk.java.net/shenandoah/pull/52