fix possible race condition

Author: mredolatti

splitio/push/sse.py

@@ -159,7 +159,7 @@ def start(self, url, extra_headers=None, timeout=socket._GLOBAL_DEFAULT_TIMEOUT)
 
     def shutdown(self):
         """Shutdown the current connection."""
-        if self._conn is None:
+        if self._conn is None or self._conn.sock is None:
             _LOGGER.warn("no sse connection has been started on this SSEClient instance. Ignoring")
             return