fix error in entry type judgment

There is no need to test compressedSize is 0 or not, just to check if the file name ends with '/'.
Following is the code snippet from Java SDK( java.util.ZipEntry)
<code>
  /**
     * Returns true if this is a directory entry. A directory entry is
     * defined to be one whose name ends with a '/'.
     * @return true if this is a directory entry
     */
    public boolean isDirectory() {
        return name.endsWith("/");
    }
</code>