chore: enhance conditional

Author: Hoa Nguyen

lib/graphql/static_validation/validator.rb

@@ -34,7 +34,7 @@ def validate(query, validate: true)
 
             # Attach legacy-style rules.
             # Only loop through rules if it has legacy-style rules
-            if legacy_rules = rules_to_use - GraphQL::StaticValidation::ALL_RULES
+            unless (legacy_rules = rules_to_use - GraphQL::StaticValidation::ALL_RULES).empty?
               legacy_rules.each do |rule_class_or_module|
                 if rule_class_or_module.method_defined?(:validate)
                   rule_class_or_module.new.validate(context)