[jdk11u-dev] RFR: 8326487: ZipFileSystem.getPath("").getFileName() returns null instead of an empty string

[xiaotaonan]

In the scenario of using ZipFileSystem, when getPath("").getFileName() returns null, change getPath("").getNameCount() to 0.

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Commit messages:
 - ZipFileSystem.getPath("").getFileName() returns null instead of an empty string

Changes: https://git.openjdk.org/jdk11u-dev/pull/2560/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2560&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326487
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2560.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2560/head:pull/2560

PR: https://git.openjdk.org/jdk11u-dev/pull/2560