Do not fail on dist-git namespaces not found in PDC
    
    This is the same idea as the previous commit. If a dist-git namespace is
    not found/supported in PDC, until now the toddler tripped and ended up
    pushing the message back to the queue and stuck in a loop.
    With this commit, we will log that this namespace is not supported and
    carry on.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>