Fixed #19257 -- Don't swallow command's KeyError in call_command

    # Load the command object.

    try:

        app_name = get_commands()[name]

    except KeyError:

        raise CommandError("Unknown command: %r" % name)

    if isinstance(app_name, BaseCommand):

        # If the command is already loaded, use it directly.

        klass = app_name

    else:

        klass = load_command_class(app_name, name)

    except KeyError:

        raise CommandError("Unknown command: %r" % name)

    # Grab out a list of defaults from the options. optparse does this for us

    # when the script runs from the command line, but since call_command can