Pipeline continue even if the message is marked as failed

[davidt99]

I have a middleware that marks certain messages as failed. The pipeline middleware is only looking whether an exception was raised and continue the chain although I had expected it to stop.
Should be an easy fix, let me know if you want me to open a PR to resolve it (if this is the desired behavior).

[Bogdanp]

I think I see what you mean. Pipelines does

        if exception is not None:
            return

whereas that should probably be something along the lines of

        if exception is not None or message.failed:
            return

Please send a PR (and don't forget to include a test!) if you're up for it!