Don't add the x-goog-conference flag if there are no simulcast senders

simulcast.js

@@ -732,6 +732,7 @@ NativeSimulcastSender.prototype.transformLocalDescription = function (desc) {
  */
 SimulcastReceiver.prototype.transformRemoteDescription = function (desc) {
 
+    if (desc && desc.sdp) {
         var sb = desc.sdp.split('\r\n');
 
         this._updateRemoteMaps(sb);
@@ -740,10 +741,11 @@ SimulcastReceiver.prototype.transformRemoteDescription = function (desc) {
         // NOTE(gp) this needs to be called after updateRemoteMaps because we need the simulcast group in the _updateRemoteMaps() method.
         this.simulcastUtils._removeSimulcastGroup(sb);
 
-    // We don't need the goog conference flag if we're not doing native
+        if (desc.sdp.indexOf('a=ssrc-group:SIM') !== -1) {
-    // simulcast, but at the receiver, we have no idea if the sender is
+            // We don't need the goog conference flag if we're not doing
-    // doing native or not-native simulcast.
+            // simulcast.
             this._ensureGoogConference(sb);
+        }
 
         desc = new RTCSessionDescription({
             type: desc.type,
@@ -751,6 +753,7 @@ SimulcastReceiver.prototype.transformRemoteDescription = function (desc) {
         });
 
         this.logger.fine(['Transformed remote description', desc.sdp].join(' '));
+    }
 
     return desc;
 };