RFR: 8246788: ZoneRules invariants can be broken

Tighten up argument checking in constructor. ------------- Commit messages: - 8246788: ZoneRules invariants can be broken Changes: https://git.openjdk.java.net/jdk/pull/2191/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2191&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8246788 Stats: 90 lines in 2 files changed: 87 ins; 0 del; 3 mod Patch: https://git.openjdk.java.net/jdk/pull/2191.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/2191/head:pull/2191 PR: https://git.openjdk.java.net/jdk/pull/2191