When doing offscreen rendering (Viewport Render or Sequencer Scene
strip) EEVEE and workbench used the wrong window coordinates. These
coordinates included the border that was not drawn.

Now the viewcamtexcofac will be reset after calculating the area to
render, as the border will be cropped.

Perhaps we need to move the viewcamtexcofacI from ED_view3d_update_viewmat to its own method.