Hide progress bar after all jobs finished.

Summary:
This is a follow-up of D3110, which keeps the progress bar showing
after parsing completed. This patch will properly hide the probress bar.

Reviewers: KDevelop, antonanikin, mwolff

Reviewed By: KDevelop, antonanikin, mwolff

Subscribers: mwolff, antonanikin, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D3537