RFR(XS): 8158360: C1: SEGV in generated code

[dean.long at oracle.com]

The (closed) bug 8158360 is caused by a misplaced null-check on one of 
our closed platforms, when compressed oops are involved. However, the 
failure was not showing up in nightly testing, so I am updating an 
existing test to cover this case.

Tested by hand and with RBT hs-nightly-comp.js.

http://cr.openjdk.java.net/~dlong/8158360/webrev/

dl