Consecutive responsive actions cause crashes

Calling two script actions (i.e. say, askYesNo) consecutively may result in messengers sending packets too soon.
Typical usage of the API would look like the below, chained together with `andThen`
```
askYesNo("...",()->{...}).andThen(()->say(...))
```
Erroneous usage would look like
```
askYesNo("...",()->{...});
say(...);
```
This should throw an exception.