message: Fix bpls when calculating get_global_array_signature() to not segfault on steps that don't have the variable.
  Previously it failed to list content of file generated by test Test.Engine.BP.WriteReadAsStreamADIOS2.Serial
diff: @@ -3039,6 +3039,8 @@ Dims get_global_array_signature(core::Engine *fp, core::IO *io,
  for (size_t step = 0; step < nsteps; step++)
  {
  minBlocks = fp->MinBlocksInfo(*variable, step);
  + if (minBlocks->Shape)
  + {
  for (size_t k = 0; k < ndim; k++)
  {
  if (firstStep)
  @@ -3051,6 +3053,7 @@ Dims get_global_array_signature(core::Engine *fp, core::IO *io,
  }
  }
  firstStep = false;
  + }
  delete minBlocks;
  }
  return dims;
  