RFR: 8287246: Check for required DSA parameters instead of letting KeyFactory provi…

[Sean Mullan]

Please review this fix to the XML Signature implementation to check for null or missing DSA parameters and throw a MarshalException before trying to create a DSA public key from its XML encoding. This will allow the code to fail earlier and not depend on the underlying provider to detect illegal or missing parameters.

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Commit messages:
 - Check for required DSA parameters instead of letting KeyFactory provider do it.

Changes: https://git.openjdk.java.net/jdk/pull/8870/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8870&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287246
  Stats: 30 lines in 1 file changed: 0 ins; 13 del; 17 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8870.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8870/head:pull/8870

PR: https://git.openjdk.java.net/jdk/pull/8870