Make sure we don't crash when stopping all jobs

Summary:
If we don't emit result, the ExecuteCompositeJob doesn't relise that
it's failing and keeps the dangling object. Calling stop all processes
would result in a crash then.

Test Plan:

• run app
• run app again
• choose to kill the first instance
• stop all processes

Reviewers: KDevelop, mwolff

Reviewed By: KDevelop, mwolff

Subscribers: mwolff, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D10874