RFR: 8306040: HttpResponseInputStream.available() returns 1 on empty stream

[Vyom Tewari]

Please review the code change for [JDK-8306040](https://bugs.openjdk.org/browse/JDK-8306040). In the overridden "available" method of "HttpResponseInputStream" we are returning 1 after exploring all the code path.

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Commit messages:
 - 8306040:HttpResponseInputStream.available() returns 1 on empty stream

Changes: https://git.openjdk.org/jdk/pull/14810/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14810&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306040
  Stats: 164 lines in 2 files changed: 162 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14810.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14810/head:pull/14810

PR: https://git.openjdk.org/jdk/pull/14810