RFR: 8029329: tmtools tests fail with NPE (in the tool) when run with G1 and FlightRecorder

[Stefan Johansson]

Hi,

Please review this fix for:
https://bugs.openjdk.java.net/browse/JDK-8029329

Webrev:
http://cr.openjdk.java.net/~sjohanss/8029329/webrev.00/

Summary:
The iterator used by the SA for walking through G1s heap regions used 
the total number of regions as the limit for hasNext. This caused a 
NullPointerException when reaching the first unallocated region. Updated 
the SA to initialize the iterator with the currently allocated number of 
regions as limit instead.

Testing:
* Tested builds through JPRT
* Ran vm.tmtools.testlist throught Aurora and observed no failures on 
the test I expected to pass.

Thanks,
Stefan