clang-tidy: fix `readability-container-size-empty` lints

Charts/Core/vtkChartLegend.cxx

IO/Core/vtkSortFileNames.cxx

IO/Exodus/vtkExodusIIReader.cxx

IO/H5Rage/H5RageAdaptor.cxx

IO/Image/vtkNrrdReader.cxx

IO/MINC/vtkMNITagPointReader.cxx

IO/MINC/vtkMNITransformReader.cxx

IO/PIO/PIOAdaptor.cxx

IO/XML/vtkXMLCompositeDataReader.cxx

IO/XML/vtkXMLHierarchicalBoxDataFileConverter.cxx

IO/Xdmf3/vtkXdmf3DataSet.cxx

IO/Xdmf3/vtkXdmf3LightDataHandler.cxx

Infovis/Core/vtkMergeColumns.cxx

Infovis/Core/vtkStringToNumeric.cxx

Infovis/Core/vtkTableToGraph.cxx

Infovis/Core/vtkWordCloud.cxx

Rendering/OpenGL2/vtkOpenGLPolyDataMapper.cxx