Correctly access OutputWidget/StandardOutputView::setTitle()

Summary:

• fix crash which was possible when removing the Run toolview after starting a unit test and then restarting a test with closed toolview
• title was not set correctly for new jobs when tabs of the OutputView were closed

Test Plan:

• start a unit test
• close the Run toolview
• start another unit test

• start a unit test, click on "Close all other output views"
• start another unit test, check the tab title

Reviewers: KDevelop, kfunk

Reviewed By: KDevelop, kfunk

Subscribers: kfunk, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D6594