Always turn cancel button off when a query is done

[sebjulliand]

The Cancel button in the editor title was not turned off when a query ended in error.
This PR turns the Cancel button off regardless of the query's end status.

How to test

• Run a query that crashes: select * from nothing
• The cancel button must be turned off
• Run a query that is successful: 'select * from qsys2.netstat_info'
• The cancel button must be turned off as well

[davecharron]

Looks good, thanks for fixing this issue.