Investigate warnings and fix them [3]

Summary:
The warnings can be found at
https://share.kde.org/index.php/s/YqpXnnjvEafO8ei

Related Google Code-In 2016 task:
https://codein.withgoogle.com/dashboard/task-instances/6201455297953792/

Test Plan: All the tests were passed

Reviewers: kfunk, ematirov, mwolff

Reviewed By: mwolff

Subscribers: mwolff, ematirov, kfunk, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D3597