RFR: 8365483: Test sun/rmi/runtime/Log/6409194/NoConsoleOutput.java sometimes fails

[David Beaumont]

The writer field of the handler needs to be re-checked for null inside the locked region before use.

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Commit messages:
 - Re-check writer after locking

Changes: https://git.openjdk.org/jdk/pull/27173/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27173&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365483
  Stats: 10 lines in 1 file changed: 5 ins; 2 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27173.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27173/head:pull/27173

PR: https://git.openjdk.org/jdk/pull/27173