hg: jdk/sandbox: 8218851: JVM crash in custom classloader stress test, JDK 12 & 13

[chris.hegarty at oracle.com]

Changeset: 7c17199fa37d
Author:    coleenp
Date:      2019-02-15 08:21 -0500
URL:       http://hg.openjdk.java.net/jdk/sandbox/rev/7c17199fa37d

8218851: JVM crash in custom classloader stress test, JDK 12 & 13
Summary: Handle NULL and unloaded constraint class in loader constraint table, also cope with unloaded but not cleaned out klass in loader constraint entries.
Reviewed-by: hseigel, huntch, stuefe

! src/hotspot/share/classfile/loaderConstraints.cpp
! src/hotspot/share/classfile/systemDictionary.cpp