RFR: 8046085: (s) inserting null key into HashMap treebin fails

[Mike Duigou]

Hello all;

This changeset corrects a problem inserting a null key into a HashMap that is using TreeBins. The root cause of the failure was diagnosed by Paul Sandoz and confirmed by Alan Bateman, Doug Lea and myself. I've prepared the changeset and a minimal test which reproduces the failure.

jbsbug: https://bugs.openjdk.java.net/browse/JDK-8046085
webrev: http://cr.openjdk.java.net/~mduigou/JDK-8046085/0/webrev/

This change will be backported to 8u-dev as quickly as possible.

Mike