If one attempted to enumerate edges that included a source or destination that wasn't yet inserted into the database, then the code would short-circuit & return no edges. This was despite the fact that YapDatabaseRelationship explicitly supports adding edges for source/destination nodes that haven't been inserted yet. This patches the bug, and includes corresponding unit tests.
See also: https://groups.google.com/forum/#!topic/yapdatabase/E7q0truTrp8
