Don't crash if connection closed before application started (#213)

Fixes #205.

daphne/http_protocol.py

@@ -160,7 +160,7 @@ class WebRequest(http.Request):
                     "server": self.server_addr,
                 })
                 # Check they didn't close an unfinished request
-                if self.content.closed:
+                if self.application_queue is None or self.content.closed:
                     # Not much we can do, the request is prematurely abandoned.
                     return
                 # Run application against request

daphne/server.py

@@ -185,6 +185,8 @@ class Server(object):
         input_queue = asyncio.Queue()
         application_instance = yield deferToThread(self.application, scope=scope)
         # Run it, and stash the future for later checking
+        if protocol not in self.connections:
+            return None
         self.connections[protocol]["application_instance"] = asyncio.ensure_future(application_instance(
             receive=input_queue.get,
             send=lambda message: self.handle_reply(protocol, message),

daphne/ws_protocol.py

@@ -75,6 +75,7 @@ class WebSocketProtocol(WebSocketServerProtocol):
                 "server": self.server_addr,
                 "subprotocols": subprotocols,
             })
+            if self.application_deferred is not None:
                 self.application_deferred.addCallback(self.applicationCreateWorked)
                 self.application_deferred.addErrback(self.applicationCreateFailed)
         except Exception as e: