Fix the creation of fresh attribute indices in DefineAttribute
Fix the creation of fresh attribute indices in DefineAttribute

This has already been fixed in the first overload that takes a `const T &value` argument, but is missing in the second overload that takes an array. Indices may currently be given out several times if attributes are deleted in between.

ornladios/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,ornladios/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,ornladios/ADIOS2,ornladios/ADIOS2,ornladios/ADIOS2