fix: sometimes video_data doesn't exist

gui/download2.py

@@ -103,13 +103,16 @@ def get_download_url(lecture, user_id, access_token):
         url = 'https://classroom-api-online.saasp.vdyoo.com/playback/v1/video/init'
         response = requests.get(url, headers=headers)
         video_data = response.json()
-        for url in video_data["videoUrls"]:
-            if ".mp4" in url:
-                video_url = url
-                success = True
-                break
-        if success is False:
-            error_message = video_data['message']
+        if "videoUrls" not in video_data:
+            success = False
+        else:
+            for url in video_data["videoUrls"]:
+                if ".mp4" in url:
+                    video_url = url
+                    success = True
+                    break
+            if success is False:
+                error_message = video_data['message']
     if live_type == 'RECORD_MODE':
         url = 'https://classroom-api-online.saasp.vdyoo.com/classroom-ai/record/v1/resources'
         response = requests.get(url, headers=headers)