[Player] Fixes duration bug for /play command

A YouTube livestream which has duration 0 would show 0:00/0:00,
which is meaningless.

src/commands/player/play.ts

@@ -49,7 +49,7 @@ async function enqueue(session: Session, tracks: Track[], pushToFront: boolean):
     if (wasPlayingAnything) {
       return { description: `Queued at position #${pushToFront ? 1 : session.queue.length}: ${videoDetails.title}` };
     }
-    const duration = videoDetails.duration != null ? getTrackDurationString(0, videoDetails.duration) : null;
+    const duration = videoDetails.duration ? getTrackDurationString(0, videoDetails.duration) : null;
     const speed = session.getPlaybackSpeed();
     const footerText = getTrackDurationAndSpeed(duration, speed);
     return {