
BUG:  Fix #3929.  Recompute FilePrefix/FilePattern if they are cleared out,
                  instead of throwing an error.

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