git: openjdk/loom: fibers: JVMTI update for NULL as current thread

[duke]

Changeset: 11a9c170
Author:    Serguei Spitsyn <serguei.spitsyn at oracle.com>
Date:      2020-08-13 05:39:00 +0000
URL:       https://git.openjdk.java.net/loom/commit/11a9c170

JVMTI update for NULL as current thread

! src/hotspot/share/prims/jvmtiEnv.cpp
! src/hotspot/share/prims/jvmtiEnvBase.cpp
! src/hotspot/share/prims/jvmtiEnvBase.hpp
+ test/hotspot/jtreg/serviceability/jvmti/vthread/NullAsCurrentThreadTest/NullAsCurrentThreadTest.java
+ test/hotspot/jtreg/serviceability/jvmti/vthread/NullAsCurrentThreadTest/libNullAsCurrentThreadTest.cpp