url: skip to-be-closed connections when pipelining (follow-up)

- Change back behavior so that pipelining is considered possible for
connections that have not yet reached the protocol level.

This is a follow-up to e5f0b1ab which had changed the behavior of
checking if pipelining is possible to ignore connections that had
'bits.close' set. Connections that have not yet reached the protocol
level also have that bit set, and we need to consider pipelining
possible on those connections.