RFR: 8303344: After JDK-8302760, G1 heap verification does not exit VM after errors

[Thomas Schatzl]

Hi all,

  please review this bug introduced in the refactoring of [JDK-8302760](https://bugs.openjdk.org/browse/JDK-8302760) where heap verification does not exit the VM because it fails to propagate errors.
Apologies for the botched refactoring.

Testing: local testing with VM changes to introduce errors

Thanks,
  Thomas

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Commit messages:
 - improve condition
 - Initial fix

Changes: https://git.openjdk.org/jdk/pull/12783/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12783&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303344
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12783.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12783/head:pull/12783

PR: https://git.openjdk.org/jdk/pull/12783