Make lyrics optional

src/main.py

@@ -32,7 +32,7 @@ def run(config):
                 audiofile.tag.images.set(
                     3, cover_art.read(), "image/png", "Cover (front)"
                 )
-            if track["lyrics"]:
+            if "lyrics" in track:
                 with open(f"{config_dir}/{track["lyrics"]}", "r", encoding="utf-8") as f:
                     text = f.read()
                     audiofile.tag.lyrics.set(text)