RFR: 8263899: HttpClient throws NPE in AuthenticationFilter when parsing www-authenticate head [v4]

[Michael McMahon]

> Could I get the following simple fix reviewed please? 
> 
> The bug is jdk.internal.net.http.AuthenticationFilter throws an NPE wrapped in an IOException if it receives a HTTP response containing a WWW-Authenticate header with no value.
> 
> Thanks,
> Michael.

Michael McMahon has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Merge branch 'master' into 8263899
 - fix whitespace error
 - updated test comment
 - Merge branch 'master' into 8263899
 - changed test to use ephemeral port
 - Initial fix

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3113/files
  - new: https://git.openjdk.java.net/jdk/pull/3113/files/7618bfd4..93b962e8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3113&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3113&range=02-03

  Stats: 2633 lines in 162 files changed: 1401 ins; 677 del; 555 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3113.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3113/head:pull/3113

PR: https://git.openjdk.java.net/jdk/pull/3113