Picking no longer works when the viewport is not the size of the whole surface

Looks like commit 782ffe1f81dba9fb68a3b6592c2e90dea8d3057d broke the use case where the viewport is not the size of the entire surface, e.g. the qt3d-sceneeditor. Picking no longer works correctly, scene is not centered at the center of the viewport, and the aspect ratio doesn't seem to be correct.