little bugfix to avoid exception on non-existing cookie

Author: Robert Aistleitner

flask_sockets.py

@@ -39,7 +39,9 @@ def __call__(self, environ, start_response):
         try:
             handler, values = adapter.match()
             environment = environ['wsgi.websocket']
-            cookie = parse_cookie(environ['HTTP_COOKIE'])
+            cookie = None
+            if 'HTTP_COOKIE' in environ:
+                cookie = parse_cookie(environ['HTTP_COOKIE'])
 
             with self.app.app_context():
                 with self.app.request_context(environ):