Add check if self.client is valid

THX Marcel.

crossechoTangoDev/Crossecho.py

@@ -109,8 +109,9 @@ class Crossecho(Device):
 
     def delete_device(self):
         # PROTECTED REGION ID(Crossecho.delete_device) ENABLED START #
-        self.client.close_session()
-        self.client.close_secure_channel()
+        if self.client is not Null:
+            self.client.close_session()
+            self.client.close_secure_channel()
         # PROTECTED REGION END #    //  Crossecho.delete_device∑
 
     # ------------------