RFR: 8377910: Minor cleanup of java/io/FileDescriptor/Sharing.java [v2]

[Brian Burkhalter]

> Null checks potentially mask a more serious, fundamental problem and should be removed to allow a `NullPointerException` to be throw if the variable is `null`.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8377910: In class OpenClose make arrays local to run method and other instance variables final

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29718/files
  - new: https://git.openjdk.org/jdk/pull/29718/files/9954cca5..9dd1613c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29718&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29718&range=00-01

  Stats: 7 lines in 1 file changed: 3 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/29718.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29718/head:pull/29718

PR: https://git.openjdk.org/jdk/pull/29718