Fixes an issue where if there's any promise already resolved or rejected...

... at the time of join, joined promise resolves instantly without waiting for all other promises to resolve.


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We, at IMVU, found out that there're some cases where joining promises don't wait till all get resolved/rejected.
And it was due to the fact that when some promises have been already resolved before joining, it instantly resolves the joined promise.

So I committed a fix with updated Specs.
Please take a look.

Thanks.
- Todd