[jdk11u-dev] RFR: 8242999: HTTP/2 client may not handle CONTINUATION frames correctly

[Martin Doerr]

Clean backport of [JDK-8242999](https://bugs.openjdk.org/browse/JDK-8242999).

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Commit messages:
 - Backport 184b43363013436302523dff203c62d5161775b7

Changes: https://git.openjdk.org/jdk11u-dev/pull/2742/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2742&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8242999
  Stats: 82 lines in 2 files changed: 60 ins; 2 del; 20 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2742.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2742/head:pull/2742

PR: https://git.openjdk.org/jdk11u-dev/pull/2742