BUG: don't allow a hierarchy node to set itself as parent

Infinite loops in the tree views were resulting when hierarchy nodes 
erroneously set their parent node id to be their own id. Printing
an error message and returning allows for easier debugging.



git-svn-id: http://svn.slicer.org/Slicer4/trunk@21645 3bd1e089-480b-0410-8dfb-8563597acbee