RFR: 7903784: NullPointerException: Cannot read the array length because the return value of "java.io.File.listFiles()" is null

[Jaikiran Pai]

Can I please get a review of this change which proposes to address NullPointerException(s) as noted in https://bugs.openjdk.org/browse/CODETOOLS-7903784?

The commit here introduces null checks to the remaining usages of `File.listFiles()` call in `ScratchDirectory`. This is similar to what we did for https://bugs.openjdk.org/browse/CODETOOLS-7903538.

No new test has been introduced given the nature of this change. Existing tests continue to pass.

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

Commit messages:
 - 7903784: NullPointerException: Cannot read the array length because the return value of "java.io.File.listFiles()" is null

Changes: https://git.openjdk.org/jtreg/pull/218/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=218&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903784
  Stats: 21 lines in 1 file changed: 16 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jtreg/pull/218.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/218/head:pull/218

PR: https://git.openjdk.org/jtreg/pull/218