ManyArray#isLoaded has changed meaning when there are no records

I’m not exactly sure when this changed but it now appears that a ManyArray with 0 records will always return false for isLoaded. In the past it would return true when there were 0 records.

The code to calculate isLoaded has changed and I am wondering if this was intentional. If so, it is kind of annoying that we now have to check ManyArray#length and ManyArray#isLoaded to determine if it is actually loaded.

Could this be related to https://github.com/emberjs/data/pull/957 ?

@teddyzeenny There is some overlap but the problem will still occur when the record is side loaded with no children in the hasMany.