Handle malformed versions in changelogs
    
    There can be anything really, so when we fail to compare the versions
    for any reason the changelog should not crash. Instead we will take
    whatever entries we collected so far (which could potentially be missing
    something), or if we have nothing so far return the whole changelog.
    
    Fixes: https://pagure.io/compose-utils/issue/71
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>