RFR: 8321818: vmTestbase/nsk/stress/strace/strace015.java failed with 'Cannot read the array length because "<local4>" is null'

[David Holmes]

Please review this simple update to the strace tests that adds a check for a null entry.

Testing:
  - self
  - tiers 1-3 (sanity)

Thanks

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Commit messages:
 - 8321818: vmTestbase/nsk/stress/strace/strace015.java failed with 'Cannot read the array length because "<local4>" is null'

Changes: https://git.openjdk.org/jdk/pull/22756/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22756&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321818
  Stats: 53 lines in 9 files changed: 45 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/22756.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22756/head:pull/22756

PR: https://git.openjdk.org/jdk/pull/22756