Fix crash when no music uploaded (null guard for track)

src/components/MusicPlayer.tsx

@@ -23,7 +23,7 @@ export default function MusicPlayer({ tracks }: { tracks: MediaItem[] }) {
   const [progress, setProgress] = useState(0)
   const audioRef = useRef<HTMLAudioElement>(null)
 
-  const track = tracks[current]
+  const track = tracks[current] ?? null
 
   useEffect(() => {
     const audio = audioRef.current
@@ -33,7 +33,7 @@ export default function MusicPlayer({ tracks }: { tracks: MediaItem[] }) {
 
   useEffect(() => {
     const audio = audioRef.current
-    if (!audio) return
+    if (!audio || !track) return
     audio.src = `/api/files/${track.filename}`
     audio.volume = muted ? 0 : volume
     if (playing) {
@@ -71,13 +71,13 @@ export default function MusicPlayer({ tracks }: { tracks: MediaItem[] }) {
     setProgress(pct)
   }
 
+  if (tracks.length === 0 || !track) return null
+
   const trackName =
     track.original_name?.replace(/\.[^/.]+$/, '') ||
     track.caption ||
     `Titel ${current + 1}`
 
-  if (tracks.length === 0) return null
-
   return (
     <>
       <audio