RFR: 8289763: Remove NULL check in CDSProtectionDomain::init_security_info()

[Ioi Lam]

Please review this trivial clean up. I removed the unnecessary NULL check, and replaced the `CHECK_(pd)` with `CHECK_NH` to make the code cleaner.

It's easier to view the changes by ignoring whitespace differences.

-------------

Commit messages:
 - 8289763: Remove NULL check in CDSProtectionDomain::init_security_info()

Changes: https://git.openjdk.org/jdk/pull/9380/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9380&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289763
  Stats: 61 lines in 1 file changed: 5 ins; 10 del; 46 mod
  Patch: https://git.openjdk.org/jdk/pull/9380.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9380/head:pull/9380

PR: https://git.openjdk.org/jdk/pull/9380