[BUGFIX] store.fetchMany should always return a promise.

I noticed that store.fetchMany is inconsistent with its return values. It returns a promise when it is fetching results but returns nothing if no valid records where given. 

This attempts to resolve this. However, I'm not exactly sure what the promise should resolve to if there is nothing to return. 

I currently have it returning the empty record set it was given. This might need to be changed.