refactor(Subtitle): Do not print "?"/"Unknown" values in str()

devine/core/tracks/subtitle.py

@@ -142,7 +142,7 @@ def __init__(self, *args: Any, codec: Subtitle.Codec, cc: bool = False, sdh: boo
     def __str__(self) -> str:
         return " | ".join(filter(bool, [
             "SUB",
-            f"[{self.codec.value}]",
+            f"[{self.codec.value}]" if self.codec else None,
             str(self.language),
             self.get_track_name()
         ]))