fix a typo

game_util.py

@@ -7,7 +7,7 @@ from fastapi import HTTPException, status
 
 def read(game: str, code: str, command: str):
     _code = os.getenv("hfs_code")
-    if +code is None:
+    if _code is None:
         raise HTTPException(status_code=status.HTTP_500_INTERNAL_SERVER_ERROR)
     if code != _code:
         raise HTTPException(status.HTTP_511_NETWORK_AUTHENTICATION_REQUIRED)