fix bug: SPACE also mutes/unmutes audio because of keyboard focus

front/src/WebRtc/AudioManager.ts

@@ -141,6 +141,9 @@ class AudioManager {
         this.audioPlayerElem.play();
 
         const muteElem = HtmlUtils.getElementByIdOrFail<HTMLInputElement>('audioplayer_mute');
+        muteElem.onmousedown = (ev: Event) => {
+            ev.preventDefault();
+        }
         muteElem.onclick = (ev: Event) => {
             this.muted = !this.muted;
             this.changeVolume();