RFR: 8320798: Console read line with zero out should zero out underlying buffer

[Naoto Sato]

It is best practice to zero out the underlying buffer after use.

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Commit messages:
 - copyright year
 - fill zero to position
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/16861/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16861&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320798
  Stats: 31 lines in 2 files changed: 30 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16861.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16861/head:pull/16861

PR: https://git.openjdk.org/jdk/pull/16861