cppcheck: reduce scope
cppcheck: reduce scope

[tomviz/DataSource.cxx:211]: (style) The scope of the variable 'extents' can be reduced.

OpenChemistry/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz,mathturtle/tomviz,OpenChemistry/tomviz,mathturtle/tomviz,mathturtle/tomviz