RFR: 8253033: CheckUnhandledOops check fails in ThreadSnapshot::initialize…

[Leonid Mesnik]

The NULL oops are corrupted by CheckUnhandledOops and should be re-written with NULL to pass testing
with -XX:+CheckUnhandledOops.

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Commit messages:
 - 8253033: CheckUnhandledOops check fails in ThreadSnapshot::initialize(...)

Changes: https://git.openjdk.java.net/jdk/pull/123/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=123&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253033
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/123.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/123/head:pull/123

PR: https://git.openjdk.java.net/jdk/pull/123