[11u] RFR Backport 8220352: Crash with assert(external_guard || result != __null) failed: Invalid JNI handle

[Simon Tooke]

Hello,

This is a request to backport 8220352, which fixes an intermittent test
failure in JVMTI tests.

The backport does not apply cleanly, because the test was converted from
C to C++.  My changes apply to the original C version, and delete the
equivalent lines in the 11u tests.

bug: https://bugs.openjdk.java.net/browse/JDK-8220352

modified webrev:
http://cr.openjdk.java.net/~stooke/webrevs/jdk-8220352-jdk11/00/

original patch: http://hg.openjdk.java.net/jdk/jdk/rev/db545bf94fbc

Thank you for your time,

-Simon