[8u] RFR 8269594: assert(_handle_mark_nesting > 1) failed: memory leak: allocating handle outside HandleMark

[Zhengyu Gu]

I would like to backport this low risk and single line patch to 8u to 
fix potential hard-to-find memory leak.

Bug: https://bugs.openjdk.java.net/browse/JDK-8269594
Patch: 
https://github.com/openjdk/jdk17/commit/4b4bef4e1e06c8efbfeb2c28e0658ce91ee9ad66

The original patch does not apply cleanly, due to undefined "self" 
variable, changed to "thread()" instead.

8u webrev: http://cr.openjdk.java.net/~zgu/JDK-8269594-8u/webrev.00/


Thanks,

-Zhengyu