BUG: DataProbe: Facilitate integration in custom view

Facilitate integration of DataProbe in custom view by
explicitly checking with the parent frame has the
expected attributes.

It prevent the processEvents from throwing errors because
there exists not text attribute on the parent.

The change checks for the attribute text and executes
the code only when the attribute exists.

This change is backward compatible.

Tested-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

From: Joshy Cyriac <j.cyriac@gmail.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25709 3bd1e089-480b-0410-8dfb-8563597acbee