RFR: 8293403: JfrResolution::on_jvmci_resolution crashes when caller is null

[Doug Simon]

When the `caller` argument to `JfrResolution::on_jvmci_resolution` is null, the method should raise an `IllegalAccessError` instead of crashing with a SIGSEGV.

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Commit messages:
 - handle nullptr for caller argument in JfrResolution::on_jvmci_resolution

Changes: https://git.openjdk.org/jdk/pull/10180/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10180&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293403
  Stats: 10 lines in 2 files changed: 8 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/10180.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10180/head:pull/10180

PR: https://git.openjdk.org/jdk/pull/10180