Fix a segmentation fault that occurred during the interpolation from fine to coarse
In https://git.rz.tu-bs.de/irmb/VirtualFluids_dev/-/merge_requests/150 a new variable offFCBulk for the interpolation from fine to coarse (FC) was added. The goal was to make it more similar to the coarse-to-fine interpolation (CF).
The routine for setting this variable was still missing, resulting in a segmentation fault when using RefinementAndExchange_streams_exchangeInterface.