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

[William Kemper]

> 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

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

Changes:
  - all: https://git.openjdk.java.net/shenandoah/pull/52/files
  - new: https://git.openjdk.java.net/shenandoah/pull/52/files/e2e979bb..1236af75

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=52&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=52&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/52.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/52/head:pull/52

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