hg: shenandoah/jdk8/hotspot: [backport] 8237632: Shenandoah: accept NULL fwdptr to cooperate with JVMTI and JFR

[zgu at redhat.com]

Changeset: 6cb89922d316
Author:    zgu
Date:      2020-02-26 15:32 -0500
URL:       https://hg.openjdk.java.net/shenandoah/jdk8/hotspot/rev/6cb89922d316

[backport] 8237632: Shenandoah: accept NULL fwdptr to cooperate with JVMTI and JFR
Reviewed-by: shade, rkennke

! src/share/vm/gc_implementation/shenandoah/shenandoahBarrierSet.hpp
! src/share/vm/gc_implementation/shenandoah/shenandoahBarrierSet.inline.hpp
! src/share/vm/gc_implementation/shenandoah/shenandoahForwarding.hpp
! src/share/vm/gc_implementation/shenandoah/shenandoahForwarding.inline.hpp
! src/share/vm/gc_implementation/shenandoah/shenandoahHeap.cpp
! src/share/vm/gc_implementation/shenandoah/shenandoahRootProcessor.cpp
! src/share/vm/gc_implementation/shenandoah/shenandoahRootProcessor.hpp