RFR: 8282200: ShouldNotReachHere() reached by AsyncGetCallTrace after JDK-8280422

[Johannes Bechberger]

Fixes the mentioned bug by replacing the check in AsyncGetCallTrace using the newly introduced method `JavaThread::thread_from_jni_environment`.

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Commit messages:
 - Fix AsyncGetCallTrace bug

Changes: https://git.openjdk.java.net/jdk/pull/7559/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7559&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282200
  Stats: 25 lines in 2 files changed: 19 ins; 5 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7559.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7559/head:pull/7559

PR: https://git.openjdk.java.net/jdk/pull/7559