KPageListView: Update width on font change

Summary:
In particular its font can be changed by Breeze style that
modifies bold fonts to regular when it polishes list views.

Reviewers: cfeck, wojnilowicz, dfaure, rkflx, broulik

Reviewed By: dfaure, rkflx

Subscribers: Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D8590