Fix from stream initialvalue type

[NaridaL]

@KEIII You're right, the initial value wasn't typed correctly. I changed your PR a bit, as it isn't necessary to add a second type parameter to type it properly. Could you check this resolves problems with your use case?

[coveralls]

Coverage decreased (-0.3%) to 93.212% when pulling 47321e7 on fix-from-stream-initialvalue-type into 643c44a on master.

[KEIII]

Thanks a lot for your review. Here is some code to describe type problem:

const num$ = timer(1000).pipe(map(() => 42)); // we got 42 after 1000 ms after subscribe
const listener: IStreamListener<number> = fromStream(num$); // no initial value, no warnings
listener.current.toFixed(); // Runtime Error: TypeError: Cannot read property 'toFixed' of undefined

TypeScript say no type errors to this code. But real think is what listener.current is undefined (cause initialValue is undefined) before stream emits value.

[NaridaL]

@KEIII , OK, that should give the proper warning now, as the 1-arg fromSream is defined as:

export function fromStream<T>(observable: IObservableStream<T>): IStreamListener<T | undefined>

[NaridaL]

@mweststrate Can you publish a 5.6.0? Thanks!

[KEIII]

@NaridaL Nope, it's still no warning. The only way I was able to describe it properly was second type for initial value like #247
I got it. It works for strict mode. Thanks.