Check for session errors in attachLink

Previously attachLink did not check for session level errors, causing
link attachment to block forever in the case of an error. This change
resolves that and properly returns the error to the caller.

client.go

@@ -729,15 +729,15 @@ func attachLink(s *Session, r *Receiver, opts []LinkOption) (*link, error) {
 
 	// request handle from Session.mux
 	select {
-	case <-s.conn.done:
-		return nil, s.conn.getErr()
+	case <-s.done:
+		return nil, s.err
 	case s.allocateHandle <- l:
 	}
 
 	// wait for handle allocation
 	select {
-	case <-s.conn.done:
-		return nil, s.conn.getErr()
+	case <-s.done:
+		return nil, s.err
 	case <-l.rx:
 	}
 
@@ -773,8 +773,8 @@ func attachLink(s *Session, r *Receiver, opts []LinkOption) (*link, error) {
 	// wait for response
 	var fr frameBody
 	select {
-	case <-s.conn.done:
-		return nil, s.conn.getErr()
+	case <-s.done:
+		return nil, s.err
 	case fr = <-l.rx:
 	}
 	debug(3, "RX: %s", fr)