findbugs is unhappy

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1617965 13f79535-47bb-0310-9956-ffa450edef68
COMPRESS-285 add some tests that can only test the XZ is there case - wouldn't know how to get rid of it during tests

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1617967 13f79535-47bb-0310-9956-ffa450edef68