cds->FS and cds->o_FS are sometimes allocated different sizes

[neil-lindquist]

Describe the bug cds->FS is allocated to hold cds->nBDF * cds->fieldOffsetSum dfloats, while cds->o_FS is allocated to hold cds->nEXT * cds->fieldOffsetSum dfloats. This can cause a segfault when nBDF != nEXT.

See: https://github.com/Nek5000/nekRS/blob/next/src/core/setup.cpp#L966 https://github.com/Nek5000/nekRS/blob/next/src/core/setup.cpp#L1021

To Reproduce NekRS segfaulted when running a test case with the tombo2 timestepper and not setting the extrapolation.

Expected behavior NekRS should not segfault

Desktop (please complete the following information):

• Summit
• Version: discovered in a fork of cb353e7, but present in the source code of the next branch