mpv: disable subs-fallback

No more having non-Japanese subtitles appear on certain videos.

Author: donovanglover

home/mpv.nix

@@ -48,6 +48,7 @@ in
       autofit = "65%";
 
       slang = "jp,jpn,japanese";
+      subs-fallback = false;
 
       inherit input-ipc-server;
     };