Add a test case for when re hydrating an aggregate right after snapshotting it with another repository

[AGiorgetti]

Looking at the code in OptimisticEventStream.OptimisticEventStream
if (minRevision > 0 && _committed.Count == 0)
{
throw new StreamNotFoundException();
}

we can have a error in the following case:

• create an aggregate
• add some events
• snapshot it.

destroy the repository and its cache

• reload the aggregate from a new repository