close ws channel if can't accept

freqtrade/rpc/api_server/ws/channel.py

@@ -125,9 +125,14 @@ class WebSocketChannel:
 
     async def accept(self):
         """
-        Accept the underlying websocket connection
+        Accept the underlying websocket connection,
+        if the connection has been closed before we can
+        accept, just close the channel.
         """
+        try:
             return await self._websocket.accept()
+        except RuntimeError:
+            await self.close()
 
     async def close(self):
         """
@@ -172,6 +177,7 @@ class WebSocketChannel:
         :param **kwargs: Any extra kwargs to pass to gather
         """
 
+        if not self.is_closed():
             # Wrap the coros into tasks if they aren't already
             self._channel_tasks = [
                 task if isinstance(task, asyncio.Task) else asyncio.create_task(task)