Updated RatableBehavior::calculateRating()
Updated RatableBehavior::calculateRating()

Fixed issue where unnecessary Model::save() is called when the $saveToField does not exist in the model schema.

Not checking the model schema for $saveToField would cause two Model::exists() calls - one in Model::save() and one in Model::invalidFields() - and finally an UPDATE statement which would merely updated the `modified` field, rendering this method useless.

zuha/Ratings-Zuha-Cakephp-Plugin,ayman-alkom/cakephp-ratings,CakeDC/ratings,dereuromark/cakephp-ratings,CodeBlastr/Ratings