RFR: JDK-8293626: AccessFlag::locations(ClassFileFormatVersion cffv) does not throw NPEx when parameter is null

[Joe Darcy]

Small fixes to AccessFlag implementation.

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Commit messages:
 - JDK-8293626: AccessFlag::locations(ClassFileFormatVersion cffv) does not throw NPEx when parameter is null

Changes: https://git.openjdk.org/jdk/pull/10243/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10243&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293626
  Stats: 33 lines in 3 files changed: 30 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10243.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10243/head:pull/10243

PR: https://git.openjdk.org/jdk/pull/10243