[jdk17u-dev] RFR: 8295872: [PPC64] JfrGetCallTrace: Need pc == nullptr check before frame constructor

[Martin Doerr]

Clean backport of [JDK-8295872](https://bugs.openjdk.org/browse/JDK-8295872). Doesn't apply automatically, because the files were renamed.

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Commit messages:
 - Backport 59a13b1856cb1cf86385874b1152531016d41c22

Changes: https://git.openjdk.org/jdk17u-dev/pull/877/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=877&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295872
  Stats: 18 lines in 2 files changed: 10 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/877.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/877/head:pull/877

PR: https://git.openjdk.org/jdk17u-dev/pull/877