Fix warnings for Smart Groups

[vpratfr]

See https://wp-customerarea.com/support/topic/smart-group-warning/#post-410013

If I like to create a new Group I receive the following error:

Warning: Illegal string offset ‘enabled’ in /var/sites/stemeseder.com/web/wp-content/plugins/customer-area-smart-groups/src/php/smart-groups-addon.class.php on line 427

Warning: Illegal string offset ‘query’ in /var/sites/stemeseder.com/web/wp-content/plugins/customer-area-smart-groups/src/php/smart-groups-addon.class.php on line 431

Warning: Cannot assign an empty string to a string offset in /var/sites/stemeseder.com/web/wp-content/plugins/customer-area-smart-groups/src/php/smart-groups-addon.class.php on line 431

Warning: Illegal string offset ‘fields’ in /var/sites/stemeseder.com/web/wp-content/plugins/customer-area-smart-groups/src/php/smart-groups-addon.class.php on line 435

If I just ignore the error and enter a new group name and press “Save Draft” the error is gone and everything is working.