Fix wrong calculation of viewPort for transitions

Viewport is calculated wrong for horizontal layout in a second instance

Task-number: QTBUG-29944
Task-Number: QTBUG-31546
Change-Id: I136ae4484278d14f796613505e3f38c65ec51ebe
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Reviewed-by: Florian Hänel <florian.haenel@basyskom.com>