RFR(XS) 8169551: Segfaults in error traces when module version is null

[harold seigel]

Hi,

Please review this small fix for JDK-8169551.

Open webrev: http://cr.openjdk.java.net/~hseigel/bug_8169551/

JBS bug: https://bugs.openjdk.java.net/browse/JDK-8169551

The fix was tested with the JCK Lang and vm tests, the JTreg hotspot, 
java/io, java/lang, and java/util tests, the nsk co-located and the 
non-co-located tests, and the RBT tier2 tests.

Thanks, Harold