Fix hidden exception in runNext

[xxshady]

Abscence of return causes a hidden exception, which is handled by catch block and then passed to the reject callback while promise is already resolved

TypeError: Cannot read properties of undefined (reading 'then')
at:

value.then(nextVal => done ? resolve() : runNext(nextVal), reject);
   // ^

You can reproduce it by following this guide and running wasm component in nodejs with this handler (and yeah, "multipleResolves" event is deprecated but it's the only way I know of to observe this bug)

process.on('multipleResolves', (...args) =>{
  console.log('multipleResolves', args)
})

[guybedford]

Thanks for fixing this!