RFR: 8011968 Kitchensink crashed with SIGSEGV in MemBaseline::baseline

[Zhengyu Gu]

This is a simple fix for NULL pointer checking.

Bug: https://jbs.oracle.com/bugs/browse/JDK-8011968
External bug: not available
Webrev: http://cr.openjdk.java.net/~zgu/8011968/webrev.00/ 
<http://cr.openjdk.java.net/%7Ezgu/8011968/webrev.00/>

Test:
   Kitchensink on Linux 32. However, this bug is very hard to reproduce. 
In fact, I have yet reproduce on any of platforms.

Thanks,

-Zhengyu