Undefined action in interpretor

[Avaq]

Related: #115
@stevenyap ran into this issue a while ago, but I was not able to reproduce it. I just experienced the same issue in one of my own projects, so I will isolate it and fix it.

.../node_modules/fluture/index.js:162
    settle(action.resolved(x));
                 ^

TypeError: Cannot read property 'resolved' of undefined
    at Timeout.resolved (.../node_modules/fluture/index.js:162:18)
    at Timeout.ontimeout [as _onTimeout] (timers.js:341:34)
    at tryOnTimeout (timers.js:232:11)
    at Timer.listOnTimeout (timers.js:202:5)