Planner throws when attempting to plan functions with zero arguments

[mattdf]

Functions with no arguments cause the planner to die with the following error:

 TypeError: Cannot read property 'dies' of undefined
      at _loop_1 (/home/dev/Programming/weiroll-calltype/node_modules/@weiroll/weiroll.js/src/planner.ts:244:39)
      at Planner.plan (/home/dev/Programming/weiroll-calltype/node_modules/@weiroll/weiroll.js/dist/planner.js:244:13)
      at Context.<anonymous> (/home/dev/Programming/weiroll-calltype/test/executor.js:130:39)