Django Channels connection closed fix

Channels can't tell if the socket is closed since different engines can
be used, so explicitly set our own closed prop to work with.

Author: SmileyChris

graphql_ws/django/consumers.py

@@ -34,6 +34,7 @@ async def connect(self):
 
     async def disconnect(self, code):
         if self.connection_context:
+            self.connection_context.closed = True
             await subscription_server.on_close(self.connection_context)
 
     async def receive_json(self, content):

graphql_ws/django/subscriptions.py

@@ -10,15 +10,15 @@
 
 
 class ChannelsConnectionContext(BaseConnectionContext):
+    def __init__(self, *args, **kwargs):
+        super(ChannelsConnectionContext, self).__init__(*args, **kwargs)
+        self.closed = False
+
     async def send(self, data):
         if self.closed:
             return
         await self.ws.send_json(data)
 
-    @property
-    def closed(self):
-        return self.ws.closed
-
     async def close(self, code):
         await self.ws.close(code=code)