Handle special case in BeginStep properly. First BeginStep when there is one step in file already loaded during Open.
Handle special case in BeginStep properly. First BeginStep when there is one step in file already loaded during Open.

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