Fixed segfault when interactor was NULL.
Fixed segfault when interactor was NULL.

sankhesh/VTK,gram526/VTK,hendradarwin/VTK,jmerkow/VTK,biddisco/VTK,hendradarwin/VTK,SimVascular/VTK,jeffbaumes/jeffbaumes-vtk,arnaudgelas/VTK,berendkleinhaneveld/VTK,candy7393/VTK,aashish24/VTK-old,sumedhasingla/VTK,candy7393/VTK,cjh1/VTK,ashray/VTK-EVM,berendkleinhaneveld/VTK,berendkleinhaneveld/VTK,jeffbaumes/jeffbaumes-vtk,arnaudgelas/VTK,naucoin/VTKSlicerWidgets,sumedhasingla/VTK,keithroe/vtkoptix,jeffbaumes/jeffbaumes-vtk,jeffbaumes/jeffbaumes-vtk,daviddoria/PointGraphsPhase1,daviddoria/PointGraphsPhase1,keithroe/vtkoptix,biddisco/VTK,collects/VTK,gram526/VTK,gram526/VTK,aashish24/VTK-old,daviddoria/PointGraphsPhase1,SimVascular/VTK,keithroe/vtkoptix,keithroe/vtkoptix,jmerkow/VTK,hendradarwin/VTK,spthaolt/VTK,daviddoria/PointGraphsPhase1,naucoin/VTKSlicerWidgets,gram526/VTK,cjh1/VTK,demarle/VTK,mspark93/VTK,jmerkow/VTK,mspark93/VTK,berendkleinhaneveld/VTK,biddisco/VTK,daviddoria/PointGraphsPhase1,sankhesh/VTK,sumedhasingla/VTK,sumedhasingla/VTK,ashray/VTK-EVM,sankhesh/VTK,johnkit/vtk-dev,demarle/VTK,candy7393/VTK,daviddoria/PointGraphsPhase1,cjh1/VTK,keithroe/vtkoptix,keithroe/vtkoptix,sumedhasingla/VTK,collects/VTK,mspark93/VTK,SimVascular/VTK,msmolens/VTK,naucoin/VTKSlicerWidgets,SimVascular/VTK,demarle/VTK,mspark93/VTK,gram526/VTK,candy7393/VTK,spthaolt/VTK,jmerkow/VTK,ashray/VTK-EVM,msmolens/VTK,jmerkow/VTK,ashray/VTK-EVM,keithroe/vtkoptix,collects/VTK,collects/VTK,SimVascular/VTK,johnkit/vtk-dev,msmolens/VTK,sumedhasingla/VTK,SimVascular/VTK,msmolens/VTK,johnkit/vtk-dev,aashish24/VTK-old,sankhesh/VTK,naucoin/VTKSlicerWidgets,spthaolt/VTK,jeffbaumes/jeffbaumes-vtk,naucoin/VTKSlicerWidgets,mspark93/VTK,jmerkow/VTK,mspark93/VTK,ashray/VTK-EVM,aashish24/VTK-old,spthaolt/VTK,gram526/VTK,sankhesh/VTK,sankhesh/VTK,arnaudgelas/VTK,johnkit/vtk-dev,aashish24/VTK-old,biddisco/VTK,johnkit/vtk-dev,candy7393/VTK,collects/VTK,ashray/VTK-EVM,naucoin/VTKSlicerWidgets,hendradarwin/VTK,arnaudgelas/VTK,arnaudgelas/VTK,arnaudgelas/VTK,johnkit/vtk-dev,gram526/VTK,sumedhasingla/VTK,demarle/VTK,demarle/VTK,ashray/VTK-EVM,ashray/VTK-EVM,SimVascular/VTK,jmerkow/VTK,msmolens/VTK,biddisco/VTK,spthaolt/VTK,aashish24/VTK-old,biddisco/VTK,msmolens/VTK,demarle/VTK,candy7393/VTK,johnkit/vtk-dev,berendkleinhaneveld/VTK,candy7393/VTK,msmolens/VTK,cjh1/VTK,gram526/VTK,spthaolt/VTK,SimVascular/VTK,mspark93/VTK,candy7393/VTK,demarle/VTK,collects/VTK,jeffbaumes/jeffbaumes-vtk,hendradarwin/VTK,sankhesh/VTK,biddisco/VTK,sumedhasingla/VTK,cjh1/VTK,cjh1/VTK,mspark93/VTK,hendradarwin/VTK,hendradarwin/VTK,berendkleinhaneveld/VTK,berendkleinhaneveld/VTK,keithroe/vtkoptix,sankhesh/VTK,msmolens/VTK,spthaolt/VTK,jmerkow/VTK,demarle/VTK