MetaIO: Add missing include <stddef.h> for ptrdiff_t
MetaIO: Add missing include <stddef.h> for ptrdiff_t

Fixes error "ptrdiff_t was not declared in this scope".

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