fix(plc4j/drivers/s7): fix NoSuchElementException when watchdog ChannelHandler was not added yet & fix exception "MessageToMessageCodec$1 must produce at least one message." & fix some typos

fix(plc4j/drivers/s7): fix NoSuchElementException when watchdog ChannelHandler was not added yet & fix exception "MessageToMessageCodec$1 must produce at least one message." & fix some typos #2033