6618335: ThreadReference.stop(null) throws NPE instead of InvalidTypeException Reviewed-by: sla

Merge

8038468: java/lang/instrument/ParallelTransformerLoader.sh fails with ClassCircularityError Summary: Add check null for loader in transform to avoid when loading a class in callback handler for boot loader, CFLH set early enough to catch classes needed during class loading, i.e. sun.misc.URLClassPath$JarLoader$2 seen in the failure. Reviewed-by: acorn, sspitsyn Contributed-by: yumin.qi@oracle.com