BUG: Fix qMRMLLayoutManagerTest1

Fix regression introduced by previous commit (ENH: Add qMRMLLayoutViewFactory).

Prior to commit(ENH: Add qMRMLLayoutViewFactory):
(1) views were not created without a viewport
and
(2) scene was re-scanned in the function "updateWidgetsFromViewNodes"
to create missing widgets if needed.

This commit restores the previous behavior by:
(1) avoiding creating a view if there are no viewport
and
(2) ensuring missing view are created when setting a new viewport

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24022 3bd1e089-480b-0410-8dfb-8563597acbee