RFR: 8287390: Cleanup Map usage in AuthenticationInfo.requestAuthentication [v2]

[Andrey Turbanov]

> `AuthenticationInfo.requestAuthentication` uses separate `HashMap`'s `get` +`put` calls.
> 
> https://github.com/openjdk/jdk/blob/176bb23de18d9ab448e77e85a9c965a7c02f2c50/src/java.base/share/classes/sun/net/www/protocol/http/AuthenticationInfo.java#L155-L165
> 
> Instead we can use the `HashMap.putIfAbsent` to make code a bit easier to follow. We know that `requests` can contain only non-null values.

Andrey Turbanov has updated the pull request incrementally with one additional commit since the last revision:

  8287390: Cleanup Map usage in AuthenticationInfo.requestAuthentication
  remove obvious assert

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8484/files
  - new: https://git.openjdk.java.net/jdk/pull/8484/files/b493aab1..f850d61f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8484&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8484&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8484.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8484/head:pull/8484

PR: https://git.openjdk.java.net/jdk/pull/8484