Don't assert that there is a parent stream
Don't assert that there is a parent stream

Some streams (HTTPStream) dynamically set up their parent stream after
construction.

Change-Id: I73613b6bbf2d361892726c7b3ad0469b0b644bb7
Reviewed-on: https://gerrit.dechocorp.com/7046
Reviewed-by: Jeremy Stanley <8cc48e55af0ea00a29d3ccf3190022dccfb4961b@decho.com>

mtanski/mordor,ccutrer/mordor,mtanski/mordor,adfin/mordor,adfin/mordor,cgaebel/mordor,cgaebel/mordor,mozy/mordor,mtanski/mordor,mozy/mordor,ccutrer/mordor,mozy/mordor,adfin/mordor,ccutrer/mordor