filters/ccs2ccsflat+ccs_flatten: nothing to do -> return orig. dump
    
    This way, we do not have to bother with stdin and/or magic file
    descriptors.  At the cons' side, the equality check is little bit
    complicated with a need to normalize both before-after variants,
    but this only affects tests anyway (that are accommodating this
    change as of now).
    
    Signed-off-by: Jan Pokorný <jpokorny@redhat.com>