vtknetcdf: Fix NULL filename case in NC_check_file_type
vtknetcdf: Fix NULL filename case in NC_check_file_type

Port fix from commit 1ed55f13 (Handle case of null filename, 2011-12-08)
to new netcdf import.

Change-Id: I00fc17789feb22adacce2fd762034ec32dfdcf49

candy7393/VTK,msmolens/VTK,msmolens/VTK,biddisco/VTK,SimVascular/VTK,demarle/VTK,SimVascular/VTK,SimVascular/VTK,johnkit/vtk-dev,johnkit/vtk-dev,biddisco/VTK,ashray/VTK-EVM,biddisco/VTK,gram526/VTK,berendkleinhaneveld/VTK,gram526/VTK,demarle/VTK,biddisco/VTK,aashish24/VTK-old,ashray/VTK-EVM,johnkit/vtk-dev,jmerkow/VTK,ashray/VTK-EVM,msmolens/VTK,aashish24/VTK-old,jmerkow/VTK,sankhesh/VTK,hendradarwin/VTK,biddisco/VTK,jmerkow/VTK,candy7393/VTK,SimVascular/VTK,jmerkow/VTK,berendkleinhaneveld/VTK,jmerkow/VTK,msmolens/VTK,candy7393/VTK,keithroe/vtkoptix,sankhesh/VTK,demarle/VTK,gram526/VTK,msmolens/VTK,hendradarwin/VTK,collects/VTK,SimVascular/VTK,mspark93/VTK,sankhesh/VTK,keithroe/vtkoptix,mspark93/VTK,gram526/VTK,gram526/VTK,mspark93/VTK,keithroe/vtkoptix,sumedhasingla/VTK,aashish24/VTK-old,berendkleinhaneveld/VTK,ashray/VTK-EVM,berendkleinhaneveld/VTK,SimVascular/VTK,collects/VTK,demarle/VTK,candy7393/VTK,jmerkow/VTK,aashish24/VTK-old,demarle/VTK,sankhesh/VTK,demarle/VTK,biddisco/VTK,demarle/VTK,sankhesh/VTK,mspark93/VTK,sumedhasingla/VTK,sumedhasingla/VTK,msmolens/VTK,mspark93/VTK,johnkit/vtk-dev,hendradarwin/VTK,sumedhasingla/VTK,gram526/VTK,gram526/VTK,sankhesh/VTK,hendradarwin/VTK,keithroe/vtkoptix,mspark93/VTK,aashish24/VTK-old,candy7393/VTK,collects/VTK,hendradarwin/VTK,jmerkow/VTK,jmerkow/VTK,hendradarwin/VTK,hendradarwin/VTK,sumedhasingla/VTK,berendkleinhaneveld/VTK,demarle/VTK,mspark93/VTK,SimVascular/VTK,ashray/VTK-EVM,aashish24/VTK-old,johnkit/vtk-dev,sumedhasingla/VTK,ashray/VTK-EVM,candy7393/VTK,msmolens/VTK,berendkleinhaneveld/VTK,msmolens/VTK,sumedhasingla/VTK,keithroe/vtkoptix,biddisco/VTK,berendkleinhaneveld/VTK,johnkit/vtk-dev,sankhesh/VTK,collects/VTK,sumedhasingla/VTK,collects/VTK,ashray/VTK-EVM,gram526/VTK,candy7393/VTK,keithroe/vtkoptix,sankhesh/VTK,candy7393/VTK,johnkit/vtk-dev,SimVascular/VTK,keithroe/vtkoptix,keithroe/vtkoptix,ashray/VTK-EVM,mspark93/VTK,collects/VTK