RFR: CODETOOLS-7902884: jcstress: Fix new Sonar warnings

[Aleksey Shipilev]

After recent commits, Sonar reports a few warnings. These should be fixed.

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Commit messages:
 - CODETOOLS-7902884: jcstress: Fix new Sonar warnings

Changes: https://git.openjdk.java.net/jcstress/pull/31/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=31&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902884
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/31.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/31/head:pull/31

PR: https://git.openjdk.java.net/jcstress/pull/31