Modify obj_to_dict_strategies for __slots__ handling

Update lambda function to check for attribute existence in __slots__.

Author: tpvasconcelos

deepdiff/deephash.py

@@ -400,7 +400,7 @@ def _prep_obj(self, obj: Any, parent: str, parents_ids: frozenset = EMPTY_FROZEN
             obj_to_dict_strategies.append(lambda o: o.__dict__)
 
         if hasattr(obj, "__slots__"):
-            obj_to_dict_strategies.append(lambda o: {i: getattr(o, i) for i in o.__slots__})
+            obj_to_dict_strategies.append(lambda o: {i: getattr(o, i) for i in o.__slots__ if hasattr(o, i)})
         else:
             import inspect
             obj_to_dict_strategies.append(lambda o: dict(inspect.getmembers(o, lambda m: not inspect.isroutine(m))))