RFR: 8320049: PKCS10 would not discard the cause when throw SignatureException on invalid key

[John Jiang]

When throw SignatureException on invalid key, it may be better to contain the cause exception.

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Commit messages:
 - 8320049: PKCS10 would not discard the cause when throw SignatureException on invalid key

Changes: https://git.openjdk.org/jdk/pull/16649/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16649&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320049
  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16649.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16649/head:pull/16649

PR: https://git.openjdk.org/jdk/pull/16649