RFR: 8326487: ZipFileSystem.getPath("").getFileName() returns null instead of an empty Path [v2]

[Jaikiran Pai]

> Can I please get a review of this change which proposes to fix the issue reported in https://bugs.openjdk.org/browse/JDK-8326487?
> 
> `java.nio.file.Path.getFileName()` is specified to return a non-null value for an empty path. However, the current implementation of zipfs returns null for an empty path. The commit in this PR addresses that issue in zipfs and introduces a test which reproduces the issue and verifies the fix.

Jaikiran Pai has updated the pull request incrementally with one additional commit since the last revision:

  move the test to PathOps

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29760/files
  - new: https://git.openjdk.org/jdk/pull/29760/files/4a531890..33b848a5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29760&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29760&range=00-01

  Stats: 58 lines in 2 files changed: 19 ins; 31 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/29760.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29760/head:pull/29760

PR: https://git.openjdk.org/jdk/pull/29760