Patch "speed" population of Motor.config

[rocco8773]

The "speed" key in Motor.config is populated from the Motor.motor dictionary, which is updated when commands are sent to the motor and relevant responses are received. This can lead to scenarios where Motor.motor["speed"] is None or an AckFlags enum. These both raise TypeError when forcing Motor.config["speed"] to be a float(). If this happens, the speed value now defaults to zero, 0.0.