RFR 8149790: NegativeArraySizeException with hprof

[George Triantafillou]

Please review this change to fix NegativeArraySizeException test 
failures with hprof:

JBS: https://bugs.openjdk.java.net/browse/JDK-8149790
webrev: 
http://cr.openjdk.java.net/~gtriantafill/8149790-webrev/webrev/index.html 
<http://cr.openjdk.java.net/%7Egtriantafill/8149790-webrev/webrev/index.html>

The original patch was contributed by Andreas Eriksson.  Tested locally 
on Linux-x64 and with RBT tiers 2 through 5.

Thanks.

-George