[jdk24u] RFR: 8348562: ZGC: segmentation fault due to missing node type check in barrier elision analysis

[Martin Doerr]

Clean backport of [JDK-8348562](https://bugs.openjdk.org/browse/JDK-8348562). It only adds a null check + bailout where the current implementation crashes with SIGSEGV.

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Commit messages:
 - Backport afcc2b03afc77f730300e1d92471466d56ed75fb

Changes: https://git.openjdk.org/jdk24u/pull/35/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk24u&pr=35&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348562
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk24u/pull/35.diff
  Fetch: git fetch https://git.openjdk.org/jdk24u.git pull/35/head:pull/35

PR: https://git.openjdk.org/jdk24u/pull/35