the PyDict_SetItem does not borrow a reference, so we need to decref

reported by Mark Hammon

Objects/object.c

@@ -351,6 +351,7 @@ get_inprogress_dict()
 		    Py_DECREF(inprogress);
 		    return NULL;
 		}
+		Py_DECREF(inprogress);
 	}
 	return inprogress;
 }