Don't try to reposition the ScrollView when we get a faulty height
Summary: BUG: 401960
Test Plan: Tried as explained in the bug, can't see the issue anymore
Reviewers: Kirigami, mart
Reviewed By: Kirigami, mart
Subscribers: plasma-devel
Tags: Kirigami
Differential Revision: https://phabricator.kde.org/D17562