deal with files without parent

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1617882 13f79535-47bb-0310-9956-ffa450edef68
COMPRESS-287 ignore unknown properties in 7z file headers

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1617883 13f79535-47bb-0310-9956-ffa450edef68