Fix @klausi manual review

Refer from https://www.drupal.org/node/2591327#comment-10608502

Fix @klausi manual review.

1. node_title_validation_node_validate(): $node_title_validation_config['exclude-' . $node->type]: this will throw PHP warnings if that array key is not set. You should add a check that it is actually set. Same for the other array keys that you are accessing here. Example: if a new node type is added then the array is out of sync.
2. node_title_validation_admin_form_validate(): doc block is wrong, this is not a hook. See https://www.drupal.org/coding-standards/docs#forms . Same for node_title_validation_admin_form_submit().
3. node_title_validation_admin_form_validate(): instead of doing the numeric validation yourself, you can use element_validate_integer_positive as a #element_validate callback, see
   https://api.drupal.org/api/drupal/developer!topics!forms_api_reference.h...