OAK-2049: ArrayIndexOutOfBoundsException in Segment.getRefId()
- Applying Tom's fix
- Asserting length <= buffer.length
- More aggressive tests case

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1625237 13f79535-47bb-0310-9956-ffa450edef68