No reporting of DBMS errors in CRM_Contact_Form_Search_Custom_Group::from()

The CRM_Contact_Form_Search_Custom_Group::from() method executes SQL queries for smart groups. There are a total of eleven calls to CRM_Core_DAO::executeQuery() in this method. In all eleven cases, errors reported by these calls are completely ignored, and in the case of an error, incorrect search results are returned to the user with no indication that anything is wrong. For this reason, smart groups which use saved searches with tables that don't exist in the current database give no error indication to the user, and return incorrect information.