RFR: 8283083: java.util.random L128X256MixRandom constructor fails to use byte[] seed

[Raffaello Giulietti]

Please review this tiny fix.

A test similar to the code proposed by the bug reporter has been added for the LXM group. It does not pass before the fix and passes after.

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Commit messages:
 - 8283083: java.util.random L128X256MixRandom constructor fails to use byte[] seed

Changes: https://git.openjdk.java.net/jdk/pull/8207/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8207&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283083
  Stats: 60 lines in 2 files changed: 51 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8207.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8207/head:pull/8207

PR: https://git.openjdk.java.net/jdk/pull/8207