RFR: CODETOOLS-7902911: jcstress: Fix new Sonar warnings

[Aleksey Shipilev]

Recent work introduced a few new complaints from Sonar. Let us fix them.

-------------

Commit messages:
 - CODETOOLS-7902911: jcstress: Fix new Sonar warnings

Changes: https://git.openjdk.java.net/jcstress/pull/42/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=42&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902911
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/42.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/42/head:pull/42

PR: https://git.openjdk.java.net/jcstress/pull/42