fix(prejoin): Replace the stored audio/video tracks when device list changes

When on prejoin screen, if the device list changes (devices are added or removed),
the newly created tracks do not properly replace the old ones, resulting in
errors after joining the meeting and trying to change the devices.
This change fixes the problem.

conference.js

     createLocalPresenterTrack,
     createLocalTracksF,
     destroyLocalTracks,
+    getLocalJitsiAudioTrack,
+    getLocalJitsiVideoTrack,
     isLocalVideoTrackMuted,
     isLocalTrackMuted,
     isUserInteractionRequiredForUnmute,
 import { suspendDetected } from './react/features/power-monitor';
 import {
     initPrejoin,
-    isPrejoinPageEnabled
+    isPrejoinPageEnabled,
+    isPrejoinPageVisible
 } from './react/features/prejoin';
 import { createRnnoiseProcessorPromise } from './react/features/rnnoise';
 import { toggleScreenshotCaptureEffect } from './react/features/screenshot-capture';
     /**
      * Start using provided video stream.
      * Stops previous video stream.
-     * @param {JitsiLocalTrack} [stream] new stream to use or null
+     * @param {JitsiLocalTrack} newTrack - new track to use or null
      * @returns {Promise}
      */
-    useVideoStream(newStream) {
+    useVideoStream(newTrack) {
         return new Promise((resolve, reject) => {
             _replaceLocalVideoTrackQueue.enqueue(onFinish => {
+                const state = APP.store.getState();
+
+                // When the prejoin page is displayed localVideo is not set
+                // so just replace the video track from the store with the new one.
+                if (isPrejoinPageVisible(state)) {
+                    const oldTrack = getLocalJitsiVideoTrack(state);
+
+                    return APP.store.dispatch(replaceLocalTrack(oldTrack, newTrack))
+                        .then(resolve)
+                        .catch(reject)
+                        .then(onFinish);
+                }
+
                 APP.store.dispatch(
-                replaceLocalTrack(this.localVideo, newStream, room))
+                replaceLocalTrack(this.localVideo, newTrack, room))
                     .then(() => {
-                        this.localVideo = newStream;
-                        this._setSharingScreen(newStream);
-                        if (newStream) {
-                            APP.UI.addLocalVideoStream(newStream);
+                        this.localVideo = newTrack;
+                        this._setSharingScreen(newTrack);
+                        if (newTrack) {
+                            APP.UI.addLocalVideoStream(newTrack);
                         }
                         this.setVideoMuteStatus(this.isLocalVideoMuted());
                     })
     /**
      * Start using provided audio stream.
      * Stops previous audio stream.
-     * @param {JitsiLocalTrack} [stream] new stream to use or null
+     * @param {JitsiLocalTrack} newTrack - new track to use or null
      * @returns {Promise}
      */
-    useAudioStream(newStream) {
+    useAudioStream(newTrack) {
         return new Promise((resolve, reject) => {
             _replaceLocalAudioTrackQueue.enqueue(onFinish => {
+                const state = APP.store.getState();
+
+                // When the prejoin page is displayed localAudio is not set
+                // so just replace the audio track from the store with the new one.
+                if (isPrejoinPageVisible(state)) {
+                    const oldTrack = getLocalJitsiAudioTrack(state);
+
+                    return APP.store.dispatch(replaceLocalTrack(oldTrack, newTrack))
+                        .then(resolve)
+                        .catch(reject)
+                        .then(onFinish);
+                }
+
                 APP.store.dispatch(
-                replaceLocalTrack(this.localAudio, newStream, room))
+                replaceLocalTrack(this.localAudio, newTrack, room))
                     .then(() => {
-                        this.localAudio = newStream;
+                        this.localAudio = newTrack;
                         this.setAudioMuteStatus(this.isLocalAudioMuted());
                     })
                     .then(resolve)

react/features/base/tracks/functions.js

     return track?.jitsiTrack;
 }
 
+/**
+ * Returns the stored local audio track.
+ *
+ * @param {Object} state - The redux state.
+ * @returns {Object}
+ */
+export function getLocalJitsiAudioTrack(state) {
+    const track = getLocalAudioTrack(state['features/base/tracks']);
+
+    return track?.jitsiTrack;
+}
+
 /**
  * Returns track of specified media type for specified participant id.
  *