Fix for window icon being stretched (and ugly) when window switcher uses large icons

Summary: When using a window switcher (alt + tab) that displays larger icon versions, konqueror's window icon looks ugly due to it only using a small icon which is being stretched.

Test Plan: Patch. Compile. Run, and once running alt+tab in a window switcher set to display large icons.

Reviewers: dfaure

Reviewed By: dfaure

Tags: Konqueror

Differential Revision: https://phabricator.kde.org/D26647