Protect against tracks without a stream.

rtpconn/webclient.go

@@ -368,7 +368,7 @@ func addDownTrackUnlocked(conn *rtpDownConnection, remoteTrack *rtpUpTrack) erro
 		id = remoteTrack.track.Kind().String()
 	}
 	msid := remoteTrack.track.StreamID()
-	if msid == "" {
+	if msid == "" || msid == "-" {
 		log.Println("Got track with empty msid")
 		msid = remoteTrack.conn.Label()
 	}

static/protocol.js

@@ -677,6 +677,10 @@ ServerConnection.prototype.gotOffer = async function(id, label, source, username
         };
 
         c.pc.ontrack = function(e) {
+            if(e.streams.length < 1) {
+                console.error("Got track with no stream");
+                return;
+            }
             c.stream = e.streams[0];
             let changed = recomputeUserStreams(sc, source, c);
             if(c.ondowntrack) {