[NbtkExpander] fix all compiler warnings
[NbtkExpander] fix all compiler warnings

Fix warnings about unused variables and missing return values.

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