A fatal exception if {{#get_db_data:}} querying MS SQL Server returns no results.

self::formatErrorMessages( $connector->errors() ) fails, if $connector->errors() is null.

Details: https://www.mediawiki.org/wiki/Extension_talk:External_Data#Fatal_exception_of_type_%22TypeError%22_if_get_db_data_has_no_results.

The proposed solution is to return an error message for empty result sets, unless errors are suppressed.