EventCalendar - if there's a problem will install 2 settings/config rows in database

I installed civicrm extension eventCalendar, but got some sort of error (not listed here). The install button was still active, I installed again and the extension was installed, but with 2 rows for domain_id showevents and eventcalendarsetting in the table civicrm_navigation. Install.sql doesn't check if the rows already exist in the database.