Do not try to send if closed

Author: blink1073

ipykernel/iostream.py

@@ -226,6 +226,9 @@ def send_multipart(self, *args, **kwargs):
 
     def _really_send(self, msg, *args, **kwargs):
         """The callback that actually sends messages"""
+        if self.closed:
+            return
+
         mp_mode = self._check_mp_mode()
 
         if mp_mode != CHILD: