Fix getVttUrlFromSubtitles not correct.

fetchYoutubeSubtitle.py

@@ -5,9 +5,9 @@ import yt_dlp
 def getVttUrlFromSubtitles(item, lang='en', vttType="vtt"):
     langs = item.keys()
     key = lang if lang in langs else ('en' if 'en' in langs else list(langs)[0] )
-    for item in langs[key]:
-        if(item.get("ext") == vttType):
-            return item.get("url")
+    for subtitle in item[key]:
+        if(subtitle.get("ext") == vttType):
+            return subtitle.get("url")
     return None
 
 async def fetchSubtitle(url: str, lang: Optional[str] = 'en', vttType="vtt") -> Optional[str]: