RFR: 8257769: Cipher.getParameters() throws NPE for ChaCha20-Poly1305

[Jamil Nimeh]

This fix corrects a problem where ChaCha20-Poly1305 objects prior to init throw NPE when getParameters() is called.  It will now generate parameters containing a random nonce on each pre-init call to getParameters(). Post-initialization calls to the getParameters() method will always return the same set of parameters until the next initialization occurs.

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Commit messages:
 - 8257769: Cipher.getParameters() throws NPE for ChaCha20-Poly1305

Changes: https://git.openjdk.java.net/jdk/pull/1644/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1644&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257769
  Stats: 113 lines in 2 files changed: 111 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1644.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1644/head:pull/1644

PR: https://git.openjdk.java.net/jdk/pull/1644