RFR: 8344903: Test TestJhsdbJstackPrintVMLocks.java intermittemt fails getProcess() is null

[SendaoYan]

Hi all,
The newly added test `test/hotspot/jtreg/serviceability/sa/TestJhsdbJstackPrintVMLocks.java` intermittent fails `the return value of "jdk.test.lib.apps.LingeredApp.getProcess()" is null`. This PR check `getProcess()` is null or not before invoke `destroyForcibly`. Test-fix only, the change has been verified locally, no risk.

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Commit messages:
 - 8344903: Test TestJhsdbJstackPrintVMLocks.java intermittemt fails getProcess() is null
 - 8344903: Test TestJhsdbJstackPrintVMLocks.java intermittemt fails getProcess() is null

Changes: https://git.openjdk.org/jdk/pull/22342/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22342&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344903
  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22342.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22342/head:pull/22342

PR: https://git.openjdk.org/jdk/pull/22342