TOOLS/youtube-dl_mpv: allow playing multiple URLs

Unfortunately this also means you can't pass extra mpv options after the
URL anymore. You can prefix the script with MPV='mpv --options' though.

TOOLS/youtube-dl_mpv.sh

@@ -14,14 +14,12 @@ video_url="$(youtube-dl \
     --user-agent="$user_agent" \
     --cookies="$cookies_file" \
     --get-url \
-    "$1")"
-
-shift
+    "$@")"
 
 $MPV \
     --cookies \
     --cookies-file="$cookies_file" \
     --user-agent="$user_agent" \
-    "$@" -- $video_url
+    -- $video_url
 
 rm -rf "$cookies_dir"