Fixes return values in _stateSetStackChanged
Fixes return values in _stateSetStackChanged

When refactoring I changed the function name but not the return value ...

cedricpinson/osgjs,cedricpinson/osgjs,jtorresfabra/osgjs,jtorresfabra/osgjs,cedricpinson/osgjs,jtorresfabra/osgjs