Fix buggy test implementation (copypaste error)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1610938 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5827: Make all Directory implementations correctly fail with IllegalArgumentException if slices are out of bounds

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1610943 13f79535-47bb-0310-9956-ffa450edef68