RFR: 8255576: (fs) Files.isHidden() throws ArrayIndexOutOfBoundsException (unix)

[Christian Stein]

This PR fixes a corner case of `Files.isHidden(Path)` where
the given path is an empty path: `Path.of("")`.

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Commit messages:
 - 8255576: (fs) Files.isHidden() throws ArrayIndexOutOfBoundsException (unix)

Changes: https://git.openjdk.java.net/jdk/pull/952/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=952&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255576
  Stats: 17 lines in 3 files changed: 14 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/952.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/952/head:pull/952

PR: https://git.openjdk.java.net/jdk/pull/952