The environment can now close right after being instantiated (#4071)

com.unity.ml-agents/Runtime/Academy.cs

                         port = port
                     }
                 );
+                Communicator.QuitCommandReceived += OnQuitCommandReceived;
+                Communicator.ResetCommandReceived += OnResetCommand;
             }
 
             if (Communicator != null)
                         "Will perform inference instead."
                     );
                     Communicator = null;
-                }
-
-                if (Communicator != null)
-                {
-                    Communicator.QuitCommandReceived += OnQuitCommandReceived;
-                    Communicator.ResetCommandReceived += OnResetCommand;
                 }
             }
 

com.unity.ml-agents/Runtime/Communicator/RpcCommunicator.cs

 
             m_Client = new UnityToExternalProto.UnityToExternalProtoClient(channel);
             var result = m_Client.Exchange(WrapMessage(unityOutput, 200));
-            unityInput = m_Client.Exchange(WrapMessage(null, 200)).UnityInput;
+            var inputMessage = m_Client.Exchange(WrapMessage(null, 200));
+            unityInput = inputMessage.UnityInput;
+            if (result.Header.Status != 200 || inputMessage.Header.Status != 200)
+            {
+                m_IsOpen = false;
+                QuitCommandReceived?.Invoke();
+            }
             return result.UnityInput;
 #else
             throw new UnityAgentsException(