BUG: Do not use QItemSelectionModel::currentRowChanged()

The signal is not reliable, ot might not be triggered at the right time.
Indeed the signal is for "key" events and has not a "selection" role.
The lack of trigger can lead to a crash due to widgets still observing
nodes that are not in the scene anymore.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23734 3bd1e089-480b-0410-8dfb-8563597acbee