Unregister comm if there is an error in publishing the comm open message

IPython/kernel/comm/comm.py

@@ -88,11 +88,14 b' class Comm(LoggingConfigurable):'
                         "and a comm_manager attached to that kernel.")
 
         comm_manager.register_comm(self)
+        try:
         self._publish_msg('comm_open',
             data=data, metadata=metadata, buffers=buffers,
-            target_name=self.target_name,
-        )
+                              target_name=self.target_name)
         self._closed = False
+        except:
+            comm_manager.unregister_comm(self)
+            raise
     
     def close(self, data=None, metadata=None, buffers=None):
         """Close the frontend-side version of this comm"""