RFR: JDK-8315042 NPE in PKCS7.parseOldSignedData

[Mark Powers]

https://bugs.openjdk.org/browse/JDK-8315042

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Commit messages:
 - first iteration

Changes: https://git.openjdk.org/jdk/pull/15844/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15844&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315042
  Stats: 23 lines in 2 files changed: 16 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/15844.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15844/head:pull/15844

PR: https://git.openjdk.org/jdk/pull/15844