Fix missing flag for multichannel addchannelaudio middleware call

Author: James Walker

speechmatics/client.py

@@ -306,7 +306,7 @@ async def _stream_channel(self, channel, stream, queue, audio_chunk_size):
 
             # seq_no is defaultdict is so the keys are created automatically
             self.seq_no[channel] += 1
-            self._call_middleware(ClientMessageType.AddChannelAudio, message)
+            self._call_middleware(ClientMessageType.AddChannelAudio, message, False)
             await queue.put(message)
         await queue.put(self._end_of_channel(channel))