[NbtkViewport] Fix after `bin-widget' branch merge.
[NbtkViewport] Fix after `bin-widget' branch merge.

pwithnall/mx,jonnylamb/mx,clutter-project/mx,jonnylamb/mx,jonnylamb/mx,clutter-project/mx,clutter-project/mx,pwithnall/mx,pwithnall/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx