minor validation tweak

Replicates graphql/graphql-js@4ad2b70

Author: Cito

src/graphql/type/validate.py

@@ -838,7 +838,7 @@ def detect_field_default_value_cycle(
 
         # Check to see if there is a cycle.
         cycle_index = self.field_path_index.get(field_str)
-        if cycle_index is not None and cycle_index > 0:
+        if cycle_index is not None:
             self.context.report_error(
                 "Invalid circular reference. The default value of Input Object"
                 f" field {field_str} references itself"