[lworld] RFR: 8271397: [lworld] SIGSEGV in ciKlass::is_subtype_of

[Tobias Hartmann]

This should fix an extremely intermittent crash (only happened once) in `ciKlass::is_subtype_of`. Similar to the checks in `Parse::do_checkcast`, we need to check for `klass->is_loaded()` before calling `is_subtype_of(klass)` in type flow analysis.

Best regards,
Tobias

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Commit messages:
 - 8271397: [lworld] SIGSEGV in ciKlass::is_subtype_of
 - 8271397: [lworld] SIGSEGV in ciKlass::is_subtype_of

Changes: https://git.openjdk.java.net/valhalla/pull/506/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=506&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271397
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/506.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/506/head:pull/506

PR: https://git.openjdk.java.net/valhalla/pull/506