Advance null check to before cast
Advance null check to before cast

Otherwise, clang analyzer thought dfunc could be nil

Change-Id: I443c31efbe38a300173ba75c739d4ab8d350abef

gram526/VTK,hendradarwin/VTK,demarle/VTK,SimVascular/VTK,gram526/VTK,gram526/VTK,ashray/VTK-EVM,candy7393/VTK,sankhesh/VTK,sumedhasingla/VTK,sumedhasingla/VTK,hendradarwin/VTK,johnkit/vtk-dev,johnkit/vtk-dev,jmerkow/VTK,demarle/VTK,demarle/VTK,candy7393/VTK,sumedhasingla/VTK,ashray/VTK-EVM,msmolens/VTK,gram526/VTK,mspark93/VTK,ashray/VTK-EVM,hendradarwin/VTK,SimVascular/VTK,keithroe/vtkoptix,jmerkow/VTK,SimVascular/VTK,keithroe/vtkoptix,mspark93/VTK,keithroe/vtkoptix,candy7393/VTK,jmerkow/VTK,msmolens/VTK,demarle/VTK,sumedhasingla/VTK,candy7393/VTK,sankhesh/VTK,candy7393/VTK,mspark93/VTK,johnkit/vtk-dev,jmerkow/VTK,mspark93/VTK,sumedhasingla/VTK,sankhesh/VTK,SimVascular/VTK,gram526/VTK,hendradarwin/VTK,msmolens/VTK,demarle/VTK,sumedhasingla/VTK,candy7393/VTK,SimVascular/VTK,sankhesh/VTK,sankhesh/VTK,msmolens/VTK,jmerkow/VTK,keithroe/vtkoptix,mspark93/VTK,johnkit/vtk-dev,ashray/VTK-EVM,keithroe/vtkoptix,keithroe/vtkoptix,sumedhasingla/VTK,SimVascular/VTK,ashray/VTK-EVM,SimVascular/VTK,mspark93/VTK,jmerkow/VTK,johnkit/vtk-dev,johnkit/vtk-dev,ashray/VTK-EVM,johnkit/vtk-dev,gram526/VTK,SimVascular/VTK,hendradarwin/VTK,msmolens/VTK,jmerkow/VTK,mspark93/VTK,msmolens/VTK,gram526/VTK,msmolens/VTK,hendradarwin/VTK,demarle/VTK,sankhesh/VTK,hendradarwin/VTK,sankhesh/VTK,keithroe/vtkoptix,candy7393/VTK,msmolens/VTK,demarle/VTK,mspark93/VTK,candy7393/VTK,sumedhasingla/VTK,ashray/VTK-EVM,sankhesh/VTK,keithroe/vtkoptix,gram526/VTK,jmerkow/VTK,ashray/VTK-EVM,demarle/VTK