[jdk22u] RFR: 8325567: jspawnhelper without args fails with segfault

[Aleksey Shipilev]

Clean backport to improve jspawnhelper resiliency and provide the grounds for later backports.

Additional testing:
 - [x] jspawnhelper no longer SEGVs when ran manually
 - [x] `java/lang/ProcessBuilder` tests pass, including new test

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

Commit messages:
 - Backport 262747094670b00ac63463a059074afa9b81d8a4

Changes: https://git.openjdk.org/jdk22u/pull/126/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk22u&pr=126&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325567
  Stats: 62 lines in 2 files changed: 62 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk22u/pull/126.diff
  Fetch: git fetch https://git.openjdk.org/jdk22u.git pull/126/head:pull/126

PR: https://git.openjdk.org/jdk22u/pull/126