hg: shenandoah/jdk: Handle null critical native array

[zgu at redhat.com]

Changeset: 314c8f455a71
Author:    zgu
Date:      2018-03-29 13:26 -0400
URL:       http://hg.openjdk.java.net/shenandoah/jdk/rev/314c8f455a71

Handle null critical native array

! src/hotspot/cpu/x86/sharedRuntime_x86_64.cpp
+ test/hotspot/jtreg/gc/shenandoah/CriticalNativeArgs.java
! test/hotspot/jtreg/gc/shenandoah/libCriticalNative.c