fix RTCPeerConnection.prototype.removeTrack to support Sender without track

Author: hthetiot

js/RTCPeerConnection.js

@@ -555,6 +555,11 @@ RTCPeerConnection.prototype.removeTrack = function (sender) {
 
 	track = sender.track;
 
+	// No sender track found
+	if (!track) {
+		return;
+	}
+
 	function matchLocalTrack(localTrack) {
 		return localTrack.id === track.id;
 	}