fix(ssrc-rewriting): Check if track exists before updating owner/sour…

…ceName.

Fixes missing audio issue when the bridge resends the full audio map even before the track for the SSRCs signaled before are created. This is possible when the RTP packets race with the thread that completed the websocket connection.

modules/xmpp/JingleSessionPC.js

@@ -1783,7 +1783,9 @@ export default class JingleSessionPC extends JingleSession {
             } else {
                 const track = this.peerconnection.getTrackBySSRC(ssrc);
 
-                if (track.getParticipantId() === owner && track.getSourceName() === source) {
+                if (!track || (track.getParticipantId() === owner && track.getSourceName() === source)) {
+                    !track && logger.warn(`Remote track for SSRC=${ssrc} hasn't been created yet,`
+                        + 'not processing the source map');
                     continue; // eslint-disable-line no-continue
                 }
                 logger.debug(`Existing SSRC re-mapped ${ssrc}: new owner=${owner}, source-name=${source}`);