Fix leaking web workers when recording new audio message

See [#5250][0].

[0]: https://github.com/signalapp/Signal-Desktop/pull/5250

js/views/recorder_view.js

@@ -58,6 +58,10 @@
       if (this.recorder.isRecording()) {
         this.recorder.cancelRecording();
       }
+
+      // Reach in and terminate the web worker used by WebAudioRecorder, otherwise
+      // it gets leaked due to a reference cycle with its onmessage listener
+      this.recorder.worker.terminate();
       this.recorder = null;
 
       if (this.interval) {