Fix showing an input box if the minimum score for PR is set to 0
    
    Up until now this was changed to a checkbox in these situations, now
    it remains an input/text field allowing to change it back to something
    else.
    
    Fixes https://pagure.io/pagure/issue/4019
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr></pingou@pingoured.fr>