fix 语法问题

app/modules/jellyfin/jellyfin.py

@@ -443,7 +443,7 @@ class Jellyfin:
         :param item_id: 在Jellyfin中的ID
         :param image_type: 图片类型，如Backdrop、Primary
         """
-        if self._playhost is None or self._playhost == "":
+        if not self._playhost:
             logger.error("Jellyfin外网播放地址未能获取或为空")
             return None