fix(conference.js): 2 tracks of the same media type

...caused by bad state as a result of timing issue around the prejoin flow.

If get user media call is delayed for a while and if user joins
the conference, when it hasn't completed then confrence.js will not assign
'localAudio' and 'localVideo' variables and will create additional media
tracks on unmute operation and add them to JitsiConference via replaceTracks
operation.

conference.js

         };
     },
 
+    /**
+     * Displays error notifications according to the state carried by {@code errors} object returned
+     * by {@link createInitialLocalTracks}.
+     * @param {Object} errors - the errors (if any) returned by {@link createInitialLocalTracks}.
+     *
+     * @returns {void}
+     * @private
+     */
+    _displayErrorsForCreateInitialLocalTracks(errors) {
+        const {
+            audioAndVideoError,
+            audioOnlyError,
+            screenSharingError,
+            videoOnlyError
+        } = errors;
+
+        // FIXME If there will be microphone error it will cover any screensharing dialog, but it's still better than in
+        // the reverse order where the screensharing dialog will sometimes be closing the microphone alert
+        // ($.prompt.close(); is called). Need to figure out dialogs chaining to fix that.
+        if (screenSharingError) {
+            this._handleScreenSharingError(screenSharingError);
+        }
+        if (audioAndVideoError || audioOnlyError) {
+            if (audioOnlyError || videoOnlyError) {
+                // If both requests for 'audio' + 'video' and 'audio' only failed, we assume that there are some
+                // problems with user's microphone and show corresponding dialog.
+                APP.store.dispatch(notifyMicError(audioOnlyError));
+                APP.store.dispatch(notifyCameraError(videoOnlyError));
+            } else {
+                // If request for 'audio' + 'video' failed, but request for 'audio' only was OK, we assume that we had
+                // problems with camera and show corresponding dialog.
+                APP.store.dispatch(notifyCameraError(audioAndVideoError));
+            }
+        }
+    },
+
     /**
      * Creates local media tracks and connects to a room. Will show error
      * dialogs in case accessing the local microphone and/or camera failed. Will
      */
     createInitialLocalTracksAndConnect(roomName, options = {}) {
         const { tryCreateLocalTracks, errors } = this.createInitialLocalTracks(options);
-        const {
-            audioAndVideoError,
-            audioOnlyError,
-            screenSharingError,
-            videoOnlyError
-        } = errors;
 
         return Promise.all([ tryCreateLocalTracks, connect(roomName) ])
             .then(([ tracks, con ]) => {
-                // FIXME If there will be microphone error it will cover any
-                // screensharing dialog, but it's still better than in
-                // the reverse order where the screensharing dialog will
-                // sometimes be closing the microphone alert ($.prompt.close();
-                // is called). Need to figure out dialogs chaining to fix that.
-                if (screenSharingError) {
-                    this._handleScreenSharingError(screenSharingError);
-                }
-                if (audioAndVideoError || audioOnlyError) {
-                    if (audioOnlyError || videoOnlyError) {
-                        // If both requests for 'audio' + 'video' and 'audio'
-                        // only failed, we assume that there are some problems
-                        // with user's microphone and show corresponding dialog.
-                        APP.store.dispatch(notifyMicError(audioOnlyError));
-                        APP.store.dispatch(notifyCameraError(videoOnlyError));
-                    } else {
-                        // If request for 'audio' + 'video' failed, but request
-                        // for 'audio' only was OK, we assume that we had
-                        // problems with camera and show corresponding dialog.
-                        APP.store.dispatch(
-                            notifyCameraError(audioAndVideoError));
-                    }
-                }
+
+                this._displayErrorsForCreateInitialLocalTracks(errors);
 
                 return [ tracks, con ];
             });
             // they may remain as empty strings.
             this._initDeviceList(true);
 
-            return APP.store.dispatch(initPrejoin(tracks, errors));
+            if (isPrejoinPageVisible(APP.store.getState())) {
+                return APP.store.dispatch(initPrejoin(tracks, errors));
+            }
+
+            logger.debug('Prejoin screen no longer displayed at the time when tracks were created');
+
+            this._displayErrorsForCreateInitialLocalTracks(errors);
+
+            return this._setLocalAudioVideoStreams(tracks);
         }
 
         const [ tracks, con ] = await this.createInitialLocalTracksAndConnect(