fix: query events_errors_summary_global_by_error safely

[jmrenouard]

The SELECT query against performance_schema.events_errors_summary_global_by_error fails when the table is not queryable or not present, causing badprint warnings in the console. Added a check against information_schema.tables to verify existence before querying.

[jmrenouard]

The implementation is delivered in the following branch: https://github.com/jmrenouard/MySQLTuner-perl/tree/v2.9.1