do not update tracks already referenced via relative paths

relative-playlist-maker.py

@@ -12,13 +12,21 @@ def main(music_folder: Path):
         with m3u.open("r") as contents:
             tracks = [Path(p).resolve() for p in contents.readlines()]
 
-        if not all(music_folder in track.parents for track in tracks):
+        if not all(
+            music_folder in track.parents 
+            if track.is_absolute() 
+            else music_folder in m3u.parent.joinpath(track).resolve().parents
+            for track in tracks
+        ):
             warning(f"{m3u} contains references to tracks that are not in {music_folder} and will be skipped")
             continue
        
         with m3u.open("w") as updated_contents:
             for track in tracks:
-                updated_contents.write(str(track.relative_to(m3u, walk_up=True)).replace("\\", "/"))
+                if track.is_absolute():
+                    updated_contents.write(str(track.relative_to(m3u, walk_up=True).as_posix()))
+                else:
+                    updated_contents.write(str(track.as_posix()))
 
 
 if __name__ == "__main__":