Handle answers in stable state.

Don't break the stream, just ignore the SDP.

rtpconn/webclient.go

@@ -554,12 +554,17 @@ func gotAnswer(c *webClient, id string, sdp string) error {
 	if down == nil {
 		return ErrUnknownId
 	}
-	err := down.pc.SetRemoteDescription(webrtc.SessionDescription{
-		Type: webrtc.SDPTypeAnswer,
-		SDP:  sdp,
-	})
-	if err != nil {
-		return err
+
+	if down.pc.SignalingState() == webrtc.SignalingStateStable {
+		log.Printf("Got answer in stable state -- this shouldn't happen")
+	} else {
+		err := down.pc.SetRemoteDescription(webrtc.SessionDescription{
+			Type: webrtc.SDPTypeAnswer,
+			SDP:  sdp,
+		})
+		if err != nil {
+			return err
+		}
 	}
 
 	for _, t := range down.tracks {
@@ -571,7 +576,7 @@ func gotAnswer(c *webClient, id string, sdp string) error {
 		}
 	}
 
-	err = down.flushICECandidates()
+	err := down.flushICECandidates()
 	if err != nil {
 		log.Printf("ICE: %v", err)
 	}