fix(JitsiConference) fix exceptions which occur after leaving the conference

Fixes issue #1476
Alternative to PR #1487

modules/RTC/JitsiRemoteTrack.js

@@ -283,6 +283,10 @@ export default class JitsiRemoteTrack extends JitsiTrack {
      * Handles track play events.
      */
     _playCallback() {
+        if (!this.conference.room) {
+            return;
+        }
+
         const type = this.isVideoTrack() ? 'video' : 'audio';
 
         const now = window.performance.now();

modules/connectivity/IceFailedHandling.js

@@ -32,6 +32,10 @@ export default class IceFailedHandling {
      * @returns {void}
      */
     _actOnIceFailed() {
+        if (!this._conference.room) {
+            return;
+        }
+
         const { enableForcedReload, enableIceRestart } = this._conference.options.config;
         const explicitlyDisabled = typeof enableIceRestart !== 'undefined' && !enableIceRestart;
         const supportsRestartByTerminate = this._conference.room.supportsRestartByTerminate();