Session.__del__ bug fix

Author: Nigel Small

neo4j/v1/session.py

@@ -430,8 +430,11 @@ def __init__(self, driver):
         self.last_cursor = None
 
     def __del__(self):
-        if not self.connection.closed:
-            self.connection.close()
+        try:
+            if not self.connection.closed:
+                self.connection.close()
+        except AttributeError:
+            pass
 
     def __enter__(self):
         return self