locally closed streams can still read

Effectively reverts 912e296

Reasons to revert to locally closed streams being readable:

Matches libp2p's yamux fork:
https://github.com/libp2p/go-yamux/blob/master/stream.go#L95-L96

Both yamux and SPDY make it clear that a locally closed stream cannot
send more data.

SPDY explicitly supports unidirectional streams where one peer is closed
(readonly) from the beginning:

https://www.chromium.org/spdy/spdy-protocol/spdy-protocol-draft3-1/#46-unidirectional-streams

stream.go

@@ -95,10 +95,12 @@ func (s *Stream) StreamID() uint32 {
 func (s *Stream) Read(b []byte) (n int, err error) {
 	defer asyncNotify(s.recvNotifyCh)
 START:
+
+	// If the stream is closed and there's no data buffered, return EOF
 	s.stateLock.Lock()
 	switch s.state {
 	case streamLocalClose:
-		fallthrough
+		// LocalClose only prohibits further local writes. Handle reads normally.
 	case streamRemoteClose:
 		fallthrough
 	case streamClosed: