Fix a property collision in django connectioncontext

Author: SmileyChris

Diff for: graphql_ws/django/consumers.py

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

Diff for: graphql_ws/django/subscriptions.py

@@ -12,13 +12,17 @@
 class ChannelsConnectionContext(BaseConnectionContext):
     def __init__(self, *args, **kwargs):
         super(ChannelsConnectionContext, self).__init__(*args, **kwargs)
-        self.closed = False
+        self.socket_closed = False
 
     async def send(self, data):
         if self.closed:
             return
         await self.ws.send_json(data)
 
+    @property
+    def closed(self):
+        return self.socket_closed
+
     async def close(self, code):
         await self.ws.close(code=code)