RFR: JVMTI GetThreadInfo fixed to return NULL when Thread is TERMINATED

[Leonid Mesnik]

JVMTI GetThreadInfo fixed to return NULL when Thread is TERMINATED
It is a fix for both Kernel and Virtual threads

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Commit messages:
 - JVMTI GetThreadInfo fixed to return NULL when Thread is TERMINATED

Changes: https://git.openjdk.java.net/loom/pull/12/files
 Webrev: https://webrevs.openjdk.java.net/loom/12/webrev.00
  Stats: 38 lines in 3 files changed: 33 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/loom/pull/12.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/12/head:pull/12

PR: https://git.openjdk.java.net/loom/pull/12