Conform more of the codebase to strictNullChecks (#10800)

src/audio/PlaybackClock.ts

@@ -60,7 +60,7 @@ export class PlaybackClock implements IDestroyable {
     private stopped = true;
     private lastCheck = 0;
     private observable = new SimpleObservable<number[]>();
-    private timerId: number;
+    private timerId?: number;
     private clipDuration = 0;
     private placeholderDuration = 0;
 

src/audio/VoiceMessageRecording.ts

@@ -33,9 +33,9 @@ export interface IUpload {
  * This class can be used to record a single voice message.
  */
 export class VoiceMessageRecording implements IDestroyable {
-    private lastUpload: IUpload;
+    private lastUpload?: IUpload;
     private buffer = new Uint8Array(0); // use this.audioBuffer to access
-    private playback: Playback;
+    private playback?: Playback;
 
     public constructor(private matrixClient: MatrixClient, private voiceRecording: VoiceRecording) {
         this.voiceRecording.onDataAvailable = this.onDataAvailable;

src/audio/VoiceRecording.ts

@@ -243,7 +243,7 @@ export class VoiceRecording extends EventEmitter implements IDestroyable {
             return;
         }
 
-        const secondsLeft = TARGET_MAX_LENGTH - this.recorderSeconds;
+        const secondsLeft = TARGET_MAX_LENGTH - this.recorderSeconds!;
         if (secondsLeft < 0) {
             // go over to make sure we definitely capture that last frame
             // noinspection JSIgnoredPromiseFromCall - we aren't concerned with it overlapping
@@ -259,7 +259,8 @@ export class VoiceRecording extends EventEmitter implements IDestroyable {
     /**
      * {@link https://github.com/chris-rudmin/opus-recorder#instance-fields ref for recorderSeconds}
      */
-    public get recorderSeconds(): number {
+    public get recorderSeconds(): number | undefined {
+        if (!this.recorder) return undefined;
         return this.recorder.encodedSamplePosition / 48000;
     }