Cache in entity_load() breaks entity_rules_load_settings_for_op()

Using one variable for different things can be very dangerous. See the code:

  $entities = entity_load('entity_rule_setting', FALSE, $conditions);
  if ($load_rules) {
    foreach (array_keys($entities) as $entity_id) {
      $entities[$entity_id]->rules_config = rules_config_load($entities[$entity_id]->rules_config);
      // If rule didn't load unset this entity
      if (empty($entities[$entity_id]->rules_config)) {
        unset($entities[$entity_id]);
      }
    }
  }

It uses the same rules_config property to store either the string or the object. The problem arises when this entity is cached in entity_load(), so the first entity_load() call returns a string in this property, and the second entity_load() call returns the object loaded by rules_config_load(). This is the common case if you define both 'update rule' and 'validation rule' for the same entity bundle.

The proposed patch adds checking of value type of rules_config property.