Avoid a double emitResult()

Summary:
ServiceJob::setResult already does a emitResult.
Discovered with the assert created in https://phabricator.kde.org/D9862

Reviewers: #frameworks, #plasma, broulik

Reviewed By: #plasma, broulik

Subscribers: broulik, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10629