vtkPNrrdReader: Fix crash when MPI is not initialized
vtkPNrrdReader: Fix crash when MPI is not initialized

If the reader is created without MPI initialized then no Controller is
available.  This can happen when vtkNrrdReader::New() returns a
vtkPNrrdReader through the object factory in a non-MPI process.  When no
controller is available fail gracefully rather than crashing.

Change-Id: Icc9a7c0b6f57b921db6e92b3bcc7d68e649261b0

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