RFR: 7903427: jcstress: Fix Sonar warnings

[Aleksey Shipilev]

SonarCloud scan finds a few warnings in current code.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jcstress/pull/135/files
 Webrev: https://webrevs.openjdk.org/?repo=jcstress&pr=135&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903427
  Stats: 5 lines in 2 files changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jcstress/pull/135.diff
  Fetch: git fetch https://git.openjdk.org/jcstress pull/135/head:pull/135

PR: https://git.openjdk.org/jcstress/pull/135