RFR: 8331682: Slow networks/Impatient clients can potentially send unencrypted TLSv1.3 alerts that won't parse on the server [v2]

[Artur Barashev]

> https://bugs.openjdk.org/browse/JDK-8331682

Artur Barashev has updated the pull request incrementally with one additional commit since the last revision:

  - Rather than proactively scanning every packet for this unlikely scenario, we reactively check for unencrypted alert after getting the BadPaddingException
  - Add "!context.isNegotiated" check as "handshakeContext" can be non-null if server receives a Post-Handshake message
  - Update test to send "close_notify" alert after "user_cancelled" alert

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21043/files
  - new: https://git.openjdk.org/jdk/pull/21043/files/03b4089d..def7e57e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21043&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21043&range=00-01

  Stats: 75 lines in 2 files changed: 35 ins; 19 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/21043.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21043/head:pull/21043

PR: https://git.openjdk.org/jdk/pull/21043