Fix handling when specified video length is too long

pytchat/downloader/downloader.py

@@ -65,10 +65,12 @@ class Downloader:
         async def _create_block(session, pos, seektime):
             continuation = arcparam.getparam(
                 self.video_id, seektime = seektime)
+            
             url = f"{REPLAY_URL}{quote(continuation)}&pbj=1"
             async with session.get(url, headers = headers) as resp:
                 text = await resp.text()
             next_continuation, actions = parser.parse(json.loads(text))
+            if actions:
                 first = parser.get_offset(actions[0])
                 last = parser.get_offset(actions[-1])
                 if self.callback:
@@ -80,9 +82,11 @@ class Downloader:
                     first = first,
                     last = last
                 )
+
         loop = asyncio.get_event_loop()
-        self.blocks = loop.run_until_complete(
+        result = loop.run_until_complete(
             _get_blocks(self.duration, self.div))
+        self.blocks = [block for block in result if block]
         return self  
 
     def remove_duplicate_head(self):