Review Request: JDK-8049881: jstack not working on core files

[Poonam Bajaj]

The changes for "8046282: SA update" introduced this bug. The following 
changes fix the failure.

Bug: JDK-8049881 <https://bugs.openjdk.java.net/browse/JDK-8049881>: 
jstack not working on core files
Webrev: http://cr.openjdk.java.net/~poonam/8049881/webrev.00/
With these changes jstack works fine with the core files.

Thanks,
Poonam