[jdk11u-dev] RFR: 8291830: jvmti/RedefineClasses/StressRedefine failed: assert(!is_null(v)) failed: narrow klass value can never be zero

[Lutz Schmidt]

Fix request [11u] 

I backport this for parity with 11.0.21-oracle. The change does not at all apply cleanly.

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Commit messages:
 - Backport fb6fd03233b0eb001e2995d20a079b6af31d2b9b

Changes: https://git.openjdk.org/jdk11u-dev/pull/2019/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2019&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291830
  Stats: 13 lines in 4 files changed: 4 ins; 1 del; 8 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2019.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2019/head:pull/2019

PR: https://git.openjdk.org/jdk11u-dev/pull/2019