[jdk11u-dev] RFR: 8273924: ArrayIndexOutOfBoundsException thrown in java.util.JapaneseImperialCalendar.add()

[Martin Doerr]

Clean backport of JDK-8273924.

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

Commit messages:
 - Backport d39aad92308fbc28bd2de164e331062ebf62da85

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/472/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=472&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273924
  Stats: 26 lines in 3 files changed: 24 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/472.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/472/head:pull/472

PR: https://git.openjdk.java.net/jdk11u-dev/pull/472