BUG: avoid spurious warnings from DataProbe during startup

Make sure the frame member of the widget is set before
setting up observers to avoid a situation where the processEvents
is called before setup is complete.  This avoids some spurious
warning messages during startup.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22823 3bd1e089-480b-0410-8dfb-8563597acbee