distgit: upload sources only if there are some
    
    See https://pagure.io/rpkg/issue/604
    
    Even if the bug is clearly on the python3-rpkg side, we need to adjust
    our code because the fix that is coming out in a new release is going
    to be this https://pagure.io/rpkg/c/c4f0ca4
    
    Merges: #2097