BUG: fixing a Markups merge error for the active place node

The more general activePlaceNodeID is to be used instead of a specific 
Annotations or Markups variable name.

Fixed while working on issue #3296 for the 4.3.1 release.



git-svn-id: http://svn.slicer.org/Slicer4/trunk@22422 3bd1e089-480b-0410-8dfb-8563597acbee