deriving fsm

Thanks for publishing this great module.

I want to make a derived store from fsm.

	const simpleSwitch = fsm('off', {
		off: { toggle: 'on' },
		on: { toggle: 'off' }
	});

	$: isOnReactive = $simpleSwitch === 'on' // this works
	const isOnDerived = derived(simpleSwitch, $simpleSwitch => $simpleSwitch === 'on') // this doesn't

Please take a look the following repl. https://svelte.dev/repl/5448ab6468704700ae1c2db736a0ac44?version=3.48.0

Accessing derived store from fsm with $ causes this error. Cannot read properties of undefined (reading 'unsubscribe')

Please let me know if I am wrong in any way. Thanks.

[kenkunz]

Apologies for not merging #9 sooner – I had intended to do this a while ago, but was busy with a work project and it fell off my radar. Just merged it and published 1.2.0 to NPM. Thank you @astanet for reporting and @morungos for the PR!

[astanet]

@morungos Thank you for your detailed research and great insights. I could not have understood it in that depth. I am glad that I was not wrong, but rather that I was able to clarify this issue. I don’t have the ability to provide a fix, but I hope this module will be even better and further accelerate development at Svelte.